Kohala (mountain)
Encyclopedia
Kohala is the oldest of five volcanoes that make up the island of Hawaii
. Kohala is an estimated one million years old—so old that it experienced, and recorded, a reversal of magnetic field 780,000 years ago. It is believed to have breached sea level
more than 500,000 years ago and to have last erupted 120,000 years ago. Kohala is 606 km² (234 sq mi) in area
and 14000 cubic kilometres (3,358.8 cu mi) in volume
, and thus constitutes just under 6% of the island of Hawaii.
The volcano is cut by multiple deep gorges, the product of thousands of years of erosion. Unlike the typical symmetry of other Hawaiian volcanoes, Kohala is shaped like a foot. Toward the end of its shield-building stage 250,000 to 300,000 years ago, a landslide
destroyed the northeast flank of the volcano, reducing its height by over 1000 m (3,281 ft) and traveling 130 km (81 mi) across the sea floor. This huge landslide may be partially responsible for the volcano's foot-like shape. In 2004, marine fossil
s on the flank of the volcano were found, far too high to have been deposited by standard ocean waves. Analysis indicated that the fossils had been deposited by a massive tsunami
approximately 120,000 years ago.
A dike
complex near the volcano's main caldera
plays a major role in Kohala's geomorphology. It separates runoff
into two major drainage basin
s, the Waipio
and Waimanu
valley
s, and it maintains the volcano's shallow water table
. Kohala supports a complex hydrological cycle
that has been exploited to provide a water supply to island residents.
Because it is so far from the nearest major landmass, the ecosystem of Kohala has experienced the phenomenon of geographic isolation, resulting in an ecosystem radically different from that of other places. Invasive species introduced by man present a problem to Kohala's ecosystem, as they push native species out of their habitat. There are several initiatives to preserve Kohala's ecosystem. Crops, especially sweet potato
(Ipomoea batatas), have been harvested on the leeward side of the volano for centuries as well. The northern part of the island is named after the mountain, with two district
s named North and South Kohala. King Kamehameha I
, the first King of the Kingdom of Hawaii
, was born in North Kohala
, near Hawi.
more than 500,000 years ago. Beginning 300,000 years ago, the rate of eruption slowly decreased over a long period of time to a point where erosion
wore the volcano down faster than Kohala rebuilt itself through volcanic activity. Decreasing eruptions combined with increasing erosion caused Kohala to slowly weather away and subside into the ocean. The oldest lava flows that are still exposed at the surface are just under 0.78 million years old. It is difficult to determine the original size and shape of the volcano, as the southeast flank has been buried by volcanic lava flows from nearby Mauna Kea
and Mauna Loa
. However, based on a sharp increase of incline on the submarine slope of the volcano at a depth of 1000 m (3,281 ft), scientists estimate that in its prime the portion of Kohala that was above the water was more than 50 km (31 mi) wide. Geologists estimate that the volcano was once about twice its current size.
The volcano is so old that it experienced, and recorded, a reversal of magnetic polarity
(a change in the orientation of Earth's magnetic field so that the positions of the North and South poles
interchange) that happened 780,000 years ago. Fifty different flow units in the top 140 m (459 ft) of exposed strata
in the Pololu section are of normal polarity, indicating that they were deposited within the last 0.78 million years. Radiometric dating ranged mostly from 450,000 to 320,000 years ago, although several pieces strayed lower; this indicated a period of eruptive history at the time.
Kohala was devastated by a massive landslide
between 250,000 and 300,000 years before present
. Debris from the slide was found on the ocean floor up to 130 km (81 mi) away from the volcano. Twenty kilometers wide at the shoreline, the landslide cut back to the summit of the volcano, and is partially, if not largely, responsible for the volcano losing 1000 m (3,281 ft) in height since then. The famous sea cliffs of the windward Kohala shoreline stand as evidence of the massive geologic disaster, and mark the topmost part of the debris from this ancient landslide. There are also several other unique features found on the volcano, all marks made by the decimating collapse.
Kohala is thought to have last erupted 120,000 years ago. However, several samples of a more recent date have been obtained. Two samples collected about 120 m (394 ft) apart, obtained from Waipio Valley on the volcano's east flank in 1977, were dated reliably to 60,000 years. Another double set of samples, collected from the western part in 1996, was measured to be 80,000 years in age. The samples have been treated with skepticism by the scientific community, and their ages have been directly challenged. The rocks collected from the west site have not been tested by subsequent experiments. The lava collected from the eastern site were allegedly found under a Mauna Loa lava flow, which had been previously dated to 187,000 years. The general agreement is that the flows are 120,000 years at their youngest, conceivably younger.
In 2004, unidentified marine fossils were found at the base of the volcano 6 km (4 mi) inshore. A research team led by University of Hawaii's
Gary McMurtry and Dave Tappin of the British Geological Survey in Nottingham
found that the fossils had been deposited by a massive tsunami
, 61 m (200 ft) above the current sea level. The team dated the fossils and nearby volcanic rock at about 120,000 years old. Based on the rate of Kohala's subsidence over the past 475,000 years, it was estimated that the fossils were deposited at a height of about 500 m (1,640 ft), well out of reach of storms and far above the normal sea level at the time. The timing corresponds with the last great landslide of nearby Mauna Loa
. Researchers hypothesize that the underwater landslide from the nearby volcano triggered a gigantic tsunami, which swept up coral and other small marine organisms, depositing them on the western face of Kohala. Mauna Loa, an active volcano, has since repaired its flank. Dave Tappin, a marine geologist with the British Geological Survey
believes that a "future collapse on this volcano, with the potential for mega-tsunami generation, is almost certain."
and reappears further southeast in the Hilo Ridge, as indicated by the relationship between collected lava samples. In addition, the two features align to one another more closely then does the ridge to Mauna Kea, of which it was once thought to constitute a part. The bulk of the ridge is built of volcanic rock
with reverse magnetic polarity, evidence that the volcano at least 780,000 years old. Older lava dated from the toe of the ridge was estimated to be roughly between 1.1 and 1.2 million years old.
The volcano's lava flows are sorted into two layers. The Hawi Volcanic layers were deposited in the shield stage of the volcano's life, and the younger Pololu Volcanics were deposited in the volcano's post-shield stage. The rock in the younger Hawi section, which overlies the older Pololu flows, is mostly 260 to 140 thousand years old, and composed mainly of hawaiite
and trachyte
. The separation between the two layers is not clear; the lowest layers may actually be in the Pololu section, based on their depositional patterns and low phosphorus
content. The time intervals separating the two periods of volcanic evolution were extremely brief, something first noted in 1988.
The forest-covered summit of the volcano consists of many cones which generated lava from its two rift zone
s between 240,000 and 120,000 years ago. Kohala completed its shield-building stage 245,000 years ago and has been in decline ever since. Potassium-argon dating
indicates that the volcano last erupted about 120,000 years ago in the late Pleistocene
. Kohala is currently in transition between the postshield and erosional Hawaiian volcanic stages
in the life cycle of Hawaiian volcanoes.
The United States Geological Survey has assessed the extinct Kohala as a low-risk area. The volcano is in zone 9 (bottom risk), while the border of the volcano with Mauna Kea is zone 8 (second lowest), as Mauna Kea has not produced lava flows for 4,500 years.
There is a small string of faults on and near the main summit caldera
, arranged parallel to the northern coast. The faults were originally regarded to be a direct result of the collapse; however scientists note the fault lines do not go all the way to the coast but are arranged tightly clustered around the caldera. This indicates that the fault lines may have been caused indirectly, possibly due to the sudden release of stress during the event.
Kohala is dissected by multiple, deeply eroded stream
valley
s in a west-east alignment, cutting into the flanks of the volcano. Just north of Kohala's summit there is a small ridge that separates two streams by about a quarter of a mile. The ridge dictates whether the falling rain will go southeast, and plunge into Waipi'o Valley, or northwest, down into Honokane Valley. The ridge itself is part of the northwest-southeast trending rift zone. When the volcano was still active, vertical sheets of magma, arranged in what is known as dikes
, forced their way out of the magma reservoir and intruded into the rift zone, which was weakened by the collapse. As the dikes forced their way up, they formed fractures and faults parallel to the rift zone. The exertion caused by the dikes produced a series of faults along the rift zone, forming horsts and graben
s (fault block
s). In the northern region of Kohala, the faulted structure prevents rainwater from naturally flowing northeast down the mountain slope. Instead, the rainwater flows down laterally and empties directly into the ocean. Two grabens control the flow of water into the two valleys.
The northwestern slope of Kohala has few stream valleys cut into it, the result of the rain shadow
effect—the dominant trade wind
s bring most of the rainfall to the northeastern slope of the volcano.
The valleys are more than 800 m (2,625 ft) in depth, among the oldest and largest of which are the Waipio and Waimanu valleys. The volcano stayed active well into the formation of these mountainside valleys, as illustrated by later Pololu lava flows, which separated into two directions and often flowed into Pololu Valley
. Recent seafloor mapping seems to show that the valley extends a short way into the seafloor, and it is believed the valley formed from the tumbled-out rock from the landslide.
In addition to being the primary factor behind the faulting structure, the dike complex plays another important role in the development of the enormous valleys—that of creating and maintaining the water table
. Hawaiian lava is extremely permeable and porous
. Rainwater easily seeps into the lava, creating a large lens of fresh water below the island surface. In most places, the top of the water table is just a few feet from sea level. Unlike porous lava flows, however, dikes cool underground into dense rock with few cracks and vesicles
. The dikes act as impermeable walls through which groundwater cannot flow. Rainwater that would ordinarily seep right through the ground gets trapped in the dike "reservoirs," located well above sea level. The groundwater is confined to a flow along the dike until it finds a means to escape. In Kohala, the numerous dikes near the summit inhibit groundwater
from seeping downslope to the northeast, where it naturally wants to go. Rather, the Kohala dike complex guides it northwest or southeast, down the axis of the rift zones, before the water can escape. Therefore, most of North Kohala's groundwater ends up in either the Waipi'o/Waimanu drainage or in the Honokane/Pololu drainage. The enormous amount of water routed through these areas results in a large amount of water erosion, which causes the valley walls to frequently collapse, accelerating valley development.
On the other hand, the numerous smaller, shallow shallow stream valleys between the large ones, such as Honokane Iki, 'Awini, Honopue, Waikapu, 'Apua, and Laupahoehoe, are deprived of groundwater by the orientation of the rift zone and its dikes. Without the large amount of water that is received by the bigger valleys, these valleys grow far more slowly. Meanwhile, the fault graben structure staves off stream flow near the summit, and the main caldera is affected relatively little by erosion from water.
, and near the summit lies a cloud forest, a type of rainforest that obtains much of its moisture from "cloud drip" in addition to precipitation
. These large cloud forests dominate its slopes. This biome
is rare, and contains a disproportionate percentage of the world's rare and endemic species. The soil at Kohala is nitrogen-rich
, facilitating root growth
.
The forest lies perpendicular to the prevailing trade winds, a characteristic that leads to frequent cloud formation and abundant rainfall. Thus the rain forests carpeting Kohala are vital to the supply of groundwater on the island. The role of Kohala's ecosystem in supporting water flow has long been recognized. As early as 1902, US Forester E M Griffith wrote "Forest protection means not only increasing the rainfall, but more important still, conserving the water supply. The future welfare and agricultural prosperity of the Hawaiian Islands depends upon the preservation of the forest."
Prior to the arrival of humans, the wildlife population at Kohala and on the rest of the island was isolated from other species, as it was separated from the nearest major landmass by over 2000 mi (3,219 km) of open water. The early colonizers of Kohala came by wind, storm or floating on the ocean. Successful colonizations occur on the magnitude of once every 35,000 years. The 2,000 successful ancestors that arrived at Kohala evolved into about 8,500 to 12,500 unique species, resulting in a very high ratio of the species present being found nowhere else on Earth. Only about 2.5% of the world's rainforest is cloud rainforest, making it a unique habitat as well.
The mountain supports approximately 155 native species of vertebrate
s, crustacean
s, mollusks
, and plant
s. A diverse complexion of fungi, liverwort
, and mosses further add to the variety. In fact, up to a quarter of the plants in the forest are mosses and fern
s. These work to capture the water from clouds, in turn providing microhabitats for invertebrate
s and amphibian
s, and their predators. Estimates on the water capacity of the forest range from 792 US gal (2,998 l) to 3962 US gal (14,998 l) per hectare
.
The mountain is also home to several bog
s, which exist as breaks in the cloud forests. It is believed that bogs form in low lying areas where clay
in the soil prevents proper water drainage, resulting in an accumulation of water that impedes the root systems of woody plant
s. Kohala's bogs are characterized by sedge
s, mosses of the genus Sphagnum
, and oha wai , native members of the bellflower family. Other habitats include rain forest and mesophytic
(wet) forests.
The same isolation that produced Kohala's unique ecosystem also makes it very vulnerable to invasive species
. Alien plants and feral animal
s are among the greatest threats to the local ecology. Plants like the kahili ginger (Hedychium gardnerianum) and the strawberry guava
(Psidium cattleinum) displace native species. Prior to human settlement, many major organisms such as conifers and rodent
s never made it onto the island, so the ecosystem never developed defenses against them, leaving Hawaii vulnerable to damage by hoofed animal
s, rodents, and predation
.
Kohala's native Hawaiian rain forest has a thick layer of ferns and mosses carpeting the floor, which act as sponges, absorbing water from rain and passing much of it through to the groundwater in aquifers below; when feral animals like pig
s trample the covering, the forest loses its ability to hold in water effectively, and instead of recharging the aquifer, it results in a severe loss of topsoil
, much of which ends up being dumped by streams into the ocean.
There is evidence of pre-modern agriculture
on the leeward slopes of Kohala. From 1400 to 1800, the principal crop grown at Kohala was sweet potato
(Ipomoea batatas), although there is also evidence of yam
s (Dioscorea sp.), taro
(Colocasia esculenta), banana
s (Musa hybrids), sugarcane
(Saacharum officinarum), and gourd
s of the family Cucurbitaceae
. The optimal rainfall level for the sweet potato lies between 30 to 50 in (76.2 to 127 cm) per year. A combination of factors makes the rainfall at Kohala variable both from location to location and from year to year. In addition, Kohala is buffeted by strong winds, which are directly correlated to soil erosion; ancient farmers utilized a series of earthen embarkments and stone walls to protect their crops. This technique has been shown to reduce wind by at least 20–30 percent.
In addition to walls, there are a series of stone paths that divided the farmed area into plots of variable size. These structures are unique because although many people used such systems at the time, Kohala has some of the few to survive. The leeward slopes of Kohala were used for sugar plantations in the late 19th century. The trip from the fields to the mills and then boats was mechanized by steam locomotive
in 1883. Several plantations on the mountain were consolidated into the Kohala Sugar Company by 1937. At the peak of its production, the company had 600 employees, 13000 acre (20 sq mi) of land, and a capacity of 45000 t (99,208,018 lb) of raw sugar per year. In 1975 the company finally closed down.
Kohala supports a very complex hydrological cycle
. In the early part of the 20th century, this was exploited by building surface irrigational channel
s designed to capture water at the higher elevations and distribute it to the then-extensive sugarcane
industry. In 1905, after 18 months and the loss of 17 lives, the Kohala Ditch, a vast network of flumes and ditches, measuring 22 mi (35 km) in length, was completed. Its has since come into use by ranches, farms, and homes. A portion of the ditch became a tourist attraction until it was damaged by the 2006 Hawaii earthquake
, centered just southwest of the mountain.
The Hawaii County Department of Water Supply relies on streams from Kohala to supply water to the population of the island. With increasing demand, the original surface channels have been supplemented by deep wells
designed to channel groundwater for domestic use.
In 2003 the Kohala Watershed Partnership (KWP) was formed, a voluntary group of private land owners and state managers, designed to help manage the Kohala watershed
and to protect it from threats, most especially invasive species.
Another project to raise awareness of Kohala's ecosystem is The Kohala Center, an independent, not-for-profit, community-based organization for research and education. It was established as a response to requests by island residents to create an educational and employment opportunity related to Hawaii's natural and cultural significance. The center's mission is "to respectfully engage the Island of Hawaii as an extraordinary and vibrant research and learning laboratory for humanity."
The land around Kohala is administered as two districts, North Kohala and South Kohala, of the County of Hawaii
. The beaches, parks, golf courses, and resorts in South Kohala are called "the Kohala Coast."
King Kamehameha I
, the first King of the unified Hawaiian Islands
, was born near Upolu Point
, the northern tip of Kohala. The site is within Kohala Historical Sites State Monument. The original Kamehameha Statue
stands in front of the community center in Kapaau, and replicas of the statue are found at Aliiōlani Hale
in Honolulu, and in the United States Capitol
at the Hall of Columns
in Washington, D.C.
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
. Kohala is an estimated one million years old—so old that it experienced, and recorded, a reversal of magnetic field 780,000 years ago. It is believed to have breached sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
more than 500,000 years ago and to have last erupted 120,000 years ago. Kohala is 606 km² (234 sq mi) in area
Area
Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...
and 14000 cubic kilometres (3,358.8 cu mi) in volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
, and thus constitutes just under 6% of the island of Hawaii.
The volcano is cut by multiple deep gorges, the product of thousands of years of erosion. Unlike the typical symmetry of other Hawaiian volcanoes, Kohala is shaped like a foot. Toward the end of its shield-building stage 250,000 to 300,000 years ago, a landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
destroyed the northeast flank of the volcano, reducing its height by over 1000 m (3,281 ft) and traveling 130 km (81 mi) across the sea floor. This huge landslide may be partially responsible for the volcano's foot-like shape. In 2004, marine fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s on the flank of the volcano were found, far too high to have been deposited by standard ocean waves. Analysis indicated that the fossils had been deposited by a massive tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
approximately 120,000 years ago.
A dike
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
complex near the volcano's main caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
plays a major role in Kohala's geomorphology. It separates runoff
Runoff
Run-off or runoff may refer to:* Surface runoff, the flow of water, from rain, snow melt, or other sources, over land* Runoff model , a mathematical model describing the rainfall-runoff relations of a rainfall catchment area or watershed...
into two major drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
s, the Waipio
Waipio valley
Waipio Valley is a valley located in the Hamakua District of the Big Island of Hawaii. "Waipio" means "curved water" in the Hawaiian language.It was the capital and permanent residence of many early Hawaiian alii up until the time of King Umi...
and Waimanu
Waimanu Valley
Waimanu Valley is a remote valley on the northeast coast of Hawaii island. Besides the main Waimanu Stream, it includes Waihīlau Falls on a tributary.-Description:...
valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
s, and it maintains the volcano's shallow water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
. Kohala supports a complex hydrological cycle
Water cycle
The water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at various places in the water cycle...
that has been exploited to provide a water supply to island residents.
Because it is so far from the nearest major landmass, the ecosystem of Kohala has experienced the phenomenon of geographic isolation, resulting in an ecosystem radically different from that of other places. Invasive species introduced by man present a problem to Kohala's ecosystem, as they push native species out of their habitat. There are several initiatives to preserve Kohala's ecosystem. Crops, especially sweet potato
Sweet potato
The sweet potato is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are an important root vegetable. The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of...
(Ipomoea batatas), have been harvested on the leeward side of the volano for centuries as well. The northern part of the island is named after the mountain, with two district
County (United States)
In the United States, a county is a geographic subdivision of a state , usually assigned some governmental authority. The term "county" is used in 48 of the 50 states; Louisiana is divided into parishes and Alaska into boroughs. Parishes and boroughs are called "county-equivalents" by the U.S...
s named North and South Kohala. King Kamehameha I
Kamehameha I
Kamehameha I , also known as Kamehameha the Great, conquered the Hawaiian Islands and formally established the Kingdom of Hawaii in 1810. By developing alliances with the major Pacific colonial powers, Kamehameha preserved Hawaii's independence under his rule...
, the first King of the Kingdom of Hawaii
Kingdom of Hawaii
The Kingdom of Hawaii was established during the years 1795 to 1810 with the subjugation of the smaller independent chiefdoms of Oahu, Maui, Molokai, Lānai, Kauai and Niihau by the chiefdom of Hawaii into one unified government...
, was born in North Kohala
Kohala, Hawaii
thumb|right|300px|The districts of the [[Hawaii |Big Island]]. From Northernmost, clockwise; Kohala , [[Hamakua|Hāmākua]], [[Hilo, Hawaii|Hilo]], [[Puna, Hawaii|Puna]], [[Kau, Hawaii|Kaū]], [[Kona District, Hawaii|Kona]]...
, near Hawi.
History
Studies of the volcano's lava accumulation rate have put the volcano's age at somewhere near one million years. It is believed to have breached sea levelSea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
more than 500,000 years ago. Beginning 300,000 years ago, the rate of eruption slowly decreased over a long period of time to a point where erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
wore the volcano down faster than Kohala rebuilt itself through volcanic activity. Decreasing eruptions combined with increasing erosion caused Kohala to slowly weather away and subside into the ocean. The oldest lava flows that are still exposed at the surface are just under 0.78 million years old. It is difficult to determine the original size and shape of the volcano, as the southeast flank has been buried by volcanic lava flows from nearby Mauna Kea
Mauna Kea
Mauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
and Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...
. However, based on a sharp increase of incline on the submarine slope of the volcano at a depth of 1000 m (3,281 ft), scientists estimate that in its prime the portion of Kohala that was above the water was more than 50 km (31 mi) wide. Geologists estimate that the volcano was once about twice its current size.
The volcano is so old that it experienced, and recorded, a reversal of magnetic polarity
Geomagnetic reversal
A geomagnetic reversal is a change in the Earth's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse...
(a change in the orientation of Earth's magnetic field so that the positions of the North and South poles
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
interchange) that happened 780,000 years ago. Fifty different flow units in the top 140 m (459 ft) of exposed strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
in the Pololu section are of normal polarity, indicating that they were deposited within the last 0.78 million years. Radiometric dating ranged mostly from 450,000 to 320,000 years ago, although several pieces strayed lower; this indicated a period of eruptive history at the time.
Kohala was devastated by a massive landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
between 250,000 and 300,000 years before present
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
. Debris from the slide was found on the ocean floor up to 130 km (81 mi) away from the volcano. Twenty kilometers wide at the shoreline, the landslide cut back to the summit of the volcano, and is partially, if not largely, responsible for the volcano losing 1000 m (3,281 ft) in height since then. The famous sea cliffs of the windward Kohala shoreline stand as evidence of the massive geologic disaster, and mark the topmost part of the debris from this ancient landslide. There are also several other unique features found on the volcano, all marks made by the decimating collapse.
Kohala is thought to have last erupted 120,000 years ago. However, several samples of a more recent date have been obtained. Two samples collected about 120 m (394 ft) apart, obtained from Waipio Valley on the volcano's east flank in 1977, were dated reliably to 60,000 years. Another double set of samples, collected from the western part in 1996, was measured to be 80,000 years in age. The samples have been treated with skepticism by the scientific community, and their ages have been directly challenged. The rocks collected from the west site have not been tested by subsequent experiments. The lava collected from the eastern site were allegedly found under a Mauna Loa lava flow, which had been previously dated to 187,000 years. The general agreement is that the flows are 120,000 years at their youngest, conceivably younger.
In 2004, unidentified marine fossils were found at the base of the volcano 6 km (4 mi) inshore. A research team led by University of Hawaii's
University of Hawaii
The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...
Gary McMurtry and Dave Tappin of the British Geological Survey in Nottingham
British Geological Survey
The British Geological Survey is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, but other centres...
found that the fossils had been deposited by a massive tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
, 61 m (200 ft) above the current sea level. The team dated the fossils and nearby volcanic rock at about 120,000 years old. Based on the rate of Kohala's subsidence over the past 475,000 years, it was estimated that the fossils were deposited at a height of about 500 m (1,640 ft), well out of reach of storms and far above the normal sea level at the time. The timing corresponds with the last great landslide of nearby Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...
. Researchers hypothesize that the underwater landslide from the nearby volcano triggered a gigantic tsunami, which swept up coral and other small marine organisms, depositing them on the western face of Kohala. Mauna Loa, an active volcano, has since repaired its flank. Dave Tappin, a marine geologist with the British Geological Survey
British Geological Survey
The British Geological Survey is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, but other centres...
believes that a "future collapse on this volcano, with the potential for mega-tsunami generation, is almost certain."
Structure
Kohala had two active rift zones, a characteristic common to Hawaiian volcanoes. The double ridge, shaped axially, was active in both the shield and postshield stages. The southeast rift zone passes under the nearby Mauna KeaMauna Kea
Mauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
and reappears further southeast in the Hilo Ridge, as indicated by the relationship between collected lava samples. In addition, the two features align to one another more closely then does the ridge to Mauna Kea, of which it was once thought to constitute a part. The bulk of the ridge is built of volcanic rock
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
with reverse magnetic polarity, evidence that the volcano at least 780,000 years old. Older lava dated from the toe of the ridge was estimated to be roughly between 1.1 and 1.2 million years old.
The volcano's lava flows are sorted into two layers. The Hawi Volcanic layers were deposited in the shield stage of the volcano's life, and the younger Pololu Volcanics were deposited in the volcano's post-shield stage. The rock in the younger Hawi section, which overlies the older Pololu flows, is mostly 260 to 140 thousand years old, and composed mainly of hawaiite
Hawaiite
Hawaiite is an olivine basalt with intermediate composition between alkali olivine and mugearite. It was first described at the island of Hawaii. In gemology, hawaiite is a colloquial term for Hawaii-originated peridot,which is gem-quality olivine mineral....
and trachyte
Trachyte
Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....
. The separation between the two layers is not clear; the lowest layers may actually be in the Pololu section, based on their depositional patterns and low phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
content. The time intervals separating the two periods of volcanic evolution were extremely brief, something first noted in 1988.
The forest-covered summit of the volcano consists of many cones which generated lava from its two rift zone
Rift zone
A rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...
s between 240,000 and 120,000 years ago. Kohala completed its shield-building stage 245,000 years ago and has been in decline ever since. Potassium-argon dating
Potassium-argon dating
Potassium–argon dating or K–Ar dating is a radiometric dating method used in geochronology and archeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium into argon . Potassium is a common element found in many materials, such as micas, clay minerals,...
indicates that the volcano last erupted about 120,000 years ago in the late Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
. Kohala is currently in transition between the postshield and erosional Hawaiian volcanic stages
Evolution of Hawaiian volcanoes
The fifteen volcanoes that make up the eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch across the North Pacific Ocean, called the Hawaiian-Emperor seamount chain....
in the life cycle of Hawaiian volcanoes.
The United States Geological Survey has assessed the extinct Kohala as a low-risk area. The volcano is in zone 9 (bottom risk), while the border of the volcano with Mauna Kea is zone 8 (second lowest), as Mauna Kea has not produced lava flows for 4,500 years.
Characteristics
Kohala, like other shield volcanoes, has a shallow surface slope due to the low viscosity of the lava flows that formed it. Events during and after its eruptions give the volcano several unique geomorphic features, some possibly resulting from the ancient collapse and landslide. The volcano is shaped like a foot; the northeast coast extends prominently across 20 km (12 mi) of shoreline, differing from the ordinarily smooth, rounded shape of Hawaiian volcanoes.There is a small string of faults on and near the main summit caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
, arranged parallel to the northern coast. The faults were originally regarded to be a direct result of the collapse; however scientists note the fault lines do not go all the way to the coast but are arranged tightly clustered around the caldera. This indicates that the fault lines may have been caused indirectly, possibly due to the sudden release of stress during the event.
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
valley
Dissected plateau
A dissected plateau is a plateau area that has been severely eroded so that the relief is sharp. Such an area may be referred to as mountainous, but dissected plateaus are distinguishable from orogenic mountain belts by the lack of folding, metamorphism, extensive faulting, or magmatic activity...
s in a west-east alignment, cutting into the flanks of the volcano. Just north of Kohala's summit there is a small ridge that separates two streams by about a quarter of a mile. The ridge dictates whether the falling rain will go southeast, and plunge into Waipi'o Valley, or northwest, down into Honokane Valley. The ridge itself is part of the northwest-southeast trending rift zone. When the volcano was still active, vertical sheets of magma, arranged in what is known as dikes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
, forced their way out of the magma reservoir and intruded into the rift zone, which was weakened by the collapse. As the dikes forced their way up, they formed fractures and faults parallel to the rift zone. The exertion caused by the dikes produced a series of faults along the rift zone, forming horsts and graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s (fault block
Fault-block mountain
Fault-block landforms are formed when large areas of bedrock are widely broken up by faults creating large vertical displacements of continental crust....
s). In the northern region of Kohala, the faulted structure prevents rainwater from naturally flowing northeast down the mountain slope. Instead, the rainwater flows down laterally and empties directly into the ocean. Two grabens control the flow of water into the two valleys.
The northwestern slope of Kohala has few stream valleys cut into it, the result of the rain shadow
Rain shadow
A rain shadow is a dry area on the lee side of a mountainous area. The mountains block the passage of rain-producing weather systems, casting a "shadow" of dryness behind them. As shown by the diagram to the right, the warm moist air is "pulled" by the prevailing winds over a mountain...
effect—the dominant trade wind
Trade wind
The trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator...
s bring most of the rainfall to the northeastern slope of the volcano.
The valleys are more than 800 m (2,625 ft) in depth, among the oldest and largest of which are the Waipio and Waimanu valleys. The volcano stayed active well into the formation of these mountainside valleys, as illustrated by later Pololu lava flows, which separated into two directions and often flowed into Pololu Valley
Pololu Valley
Pololū is the Northernmost of a series of erosional valleys forming the east coast of Kohala Mountain on the Island of Hawaii. The word Pololū means long spear in the Hawaiian language.- Features :...
. Recent seafloor mapping seems to show that the valley extends a short way into the seafloor, and it is believed the valley formed from the tumbled-out rock from the landslide.
In addition to being the primary factor behind the faulting structure, the dike complex plays another important role in the development of the enormous valleys—that of creating and maintaining the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
. Hawaiian lava is extremely permeable and porous
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
. Rainwater easily seeps into the lava, creating a large lens of fresh water below the island surface. In most places, the top of the water table is just a few feet from sea level. Unlike porous lava flows, however, dikes cool underground into dense rock with few cracks and vesicles
Vesicular texture
Vesicular texture is a volcanic rock texture characterised by a rock being pitted with many cavities at its surface and inside. The texture is often found in extrusive aphanitic, or glassy, igneous rock...
. The dikes act as impermeable walls through which groundwater cannot flow. Rainwater that would ordinarily seep right through the ground gets trapped in the dike "reservoirs," located well above sea level. The groundwater is confined to a flow along the dike until it finds a means to escape. In Kohala, the numerous dikes near the summit inhibit groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
from seeping downslope to the northeast, where it naturally wants to go. Rather, the Kohala dike complex guides it northwest or southeast, down the axis of the rift zones, before the water can escape. Therefore, most of North Kohala's groundwater ends up in either the Waipi'o/Waimanu drainage or in the Honokane/Pololu drainage. The enormous amount of water routed through these areas results in a large amount of water erosion, which causes the valley walls to frequently collapse, accelerating valley development.
On the other hand, the numerous smaller, shallow shallow stream valleys between the large ones, such as Honokane Iki, 'Awini, Honopue, Waikapu, 'Apua, and Laupahoehoe, are deprived of groundwater by the orientation of the rift zone and its dikes. Without the large amount of water that is received by the bigger valleys, these valleys grow far more slowly. Meanwhile, the fault graben structure staves off stream flow near the summit, and the main caldera is affected relatively little by erosion from water.
Ecology
The natural habitats in the Kohala district range across a wide rainfall gradient in a very short distance—from less than 5 in (127 mm) a year on the coast near Kawaihae, to more than 150 in (3,810 mm) a year near the summit of Kohala Mountain, a distance of just 11 mi (18 km). At the coast are remnants of dry forestsHawaiian tropical dry forests
The Hawaiian tropical dry forests are a tropical dry broadleaf forest ecoregion in the Hawaiian Islands. They cover an area of on the leeward side of the main islands and the summits of Niihau and Kahoolawe. These forests are either seasonal or sclerophyllous. Annual rainfall is less than and...
, and near the summit lies a cloud forest, a type of rainforest that obtains much of its moisture from "cloud drip" in addition to precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
. These large cloud forests dominate its slopes. This biome
Biome
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...
is rare, and contains a disproportionate percentage of the world's rare and endemic species. The soil at Kohala is nitrogen-rich
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, facilitating root growth
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
.
The forest lies perpendicular to the prevailing trade winds, a characteristic that leads to frequent cloud formation and abundant rainfall. Thus the rain forests carpeting Kohala are vital to the supply of groundwater on the island. The role of Kohala's ecosystem in supporting water flow has long been recognized. As early as 1902, US Forester E M Griffith wrote "Forest protection means not only increasing the rainfall, but more important still, conserving the water supply. The future welfare and agricultural prosperity of the Hawaiian Islands depends upon the preservation of the forest."
Prior to the arrival of humans, the wildlife population at Kohala and on the rest of the island was isolated from other species, as it was separated from the nearest major landmass by over 2000 mi (3,219 km) of open water. The early colonizers of Kohala came by wind, storm or floating on the ocean. Successful colonizations occur on the magnitude of once every 35,000 years. The 2,000 successful ancestors that arrived at Kohala evolved into about 8,500 to 12,500 unique species, resulting in a very high ratio of the species present being found nowhere else on Earth. Only about 2.5% of the world's rainforest is cloud rainforest, making it a unique habitat as well.
The mountain supports approximately 155 native species of vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, mollusks
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
, and plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s. A diverse complexion of fungi, liverwort
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
, and mosses further add to the variety. In fact, up to a quarter of the plants in the forest are mosses and fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s. These work to capture the water from clouds, in turn providing microhabitats for invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s and amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, and their predators. Estimates on the water capacity of the forest range from 792 US gal (2,998 l) to 3962 US gal (14,998 l) per hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
.
The mountain is also home to several bog
Bog
A bog, quagmire or mire is a wetland that accumulates acidic peat, a deposit of dead plant material—often mosses or, in Arctic climates, lichens....
s, which exist as breaks in the cloud forests. It is believed that bogs form in low lying areas where clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
in the soil prevents proper water drainage, resulting in an accumulation of water that impedes the root systems of woody plant
Woody plant
A woody plant is a plant that uses wood as its structural tissue. These are typically perennial plants whose stems and larger roots are reinforced with wood produced adjacent to the vascular tissues. The main stem, larger branches, and roots of these plants are usually covered by a layer of...
s. Kohala's bogs are characterized by sedge
Sedge
- Plants :* Acorus calamus, sweet flag, a plant in the Acoraceae family* Any of the plants in the family Cyperaceae- Animals :* A collective noun for several species of birds, including bitterns, cranes and herons* Sedge-fly, caddisfly- Other uses :...
s, mosses of the genus Sphagnum
Sphagnum
Sphagnum is a genus of between 151 and 350 species of mosses commonly called peat moss, due to its prevalence in peat bogs and mires. A distinction is made between sphagnum moss, the live moss growing on top of a peat bog on one hand, and sphagnum peat moss or sphagnum peat on the other, the...
, and oha wai , native members of the bellflower family. Other habitats include rain forest and mesophytic
Mesophyte
Mesophytes are terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment. An example of a mesophytic habitat would be a rural temperate meadow, which might contain Goldenrod, Clover, Oxeye Daisy, and Rosa multiflora.Mesophytes make up the largest ecological...
(wet) forests.
The same isolation that produced Kohala's unique ecosystem also makes it very vulnerable to invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
. Alien plants and feral animal
Feral
A feral organism is one that has changed from being domesticated to being wild or untamed. In the case of plants it is a movement from cultivated to uncultivated or controlled to volunteer. The introduction of feral animals or plants to their non-native regions, like any introduced species, may...
s are among the greatest threats to the local ecology. Plants like the kahili ginger (Hedychium gardnerianum) and the strawberry guava
Strawberry guava
Psidium cattleianum, named in honour of notable English horticulturist Sir William Cattley, commonly known as Cattley guava or Peruvian guava, is a small tree , bearing small red or yellow fruit, which are somewhat sour but sometimes eaten or made into jam...
(Psidium cattleinum) displace native species. Prior to human settlement, many major organisms such as conifers and rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s never made it onto the island, so the ecosystem never developed defenses against them, leaving Hawaii vulnerable to damage by hoofed animal
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s, rodents, and predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
.
Kohala's native Hawaiian rain forest has a thick layer of ferns and mosses carpeting the floor, which act as sponges, absorbing water from rain and passing much of it through to the groundwater in aquifers below; when feral animals like pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
s trample the covering, the forest loses its ability to hold in water effectively, and instead of recharging the aquifer, it results in a severe loss of topsoil
Topsoil
Topsoil is the upper, outermost layer of soil, usually the top to . It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.-Importance:...
, much of which ends up being dumped by streams into the ocean.
Human history
Neolithic Revolution
The Neolithic Revolution was the first agricultural revolution. It was the transition from hunting and gathering to agriculture and settlement. Archaeological data indicates that various forms of plants and animal domestication evolved independently in 6 separate locations worldwide circa...
on the leeward slopes of Kohala. From 1400 to 1800, the principal crop grown at Kohala was sweet potato
Sweet potato
The sweet potato is a dicotyledonous plant that belongs to the family Convolvulaceae. Its large, starchy, sweet-tasting, tuberous roots are an important root vegetable. The young leaves and shoots are sometimes eaten as greens. Of the approximately 50 genera and more than 1,000 species of...
(Ipomoea batatas), although there is also evidence of yam
Yam (vegetable)
Yam is the common name for some species in the genus Dioscorea . These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania...
s (Dioscorea sp.), taro
Taro
Taro is a common name for the corms and tubers of several plants in the family Araceae . Of these, Colocasia esculenta is the most widely cultivated, and is the subject of this article. More specifically, this article describes the 'dasheen' form of taro; another variety is called eddoe.Taro is...
(Colocasia esculenta), banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....
s (Musa hybrids), sugarcane
Sugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...
(Saacharum officinarum), and gourd
Gourd
A gourd is a plant of the family Cucurbitaceae. Gourd is occasionally used to describe crops like cucumbers, squash, luffas, and melons. The term 'gourd' however, can more specifically, refer to the plants of the two Cucurbitaceae genera Lagenaria and Cucurbita or also to their hollow dried out shell...
s of the family Cucurbitaceae
Cucurbitaceae
The plant family Cucurbitaceae consists of various squashes, melons, and gourds, including crops such as cucumber, pumpkins, luffas, and watermelons...
. The optimal rainfall level for the sweet potato lies between 30 to 50 in (76.2 to 127 cm) per year. A combination of factors makes the rainfall at Kohala variable both from location to location and from year to year. In addition, Kohala is buffeted by strong winds, which are directly correlated to soil erosion; ancient farmers utilized a series of earthen embarkments and stone walls to protect their crops. This technique has been shown to reduce wind by at least 20–30 percent.
In addition to walls, there are a series of stone paths that divided the farmed area into plots of variable size. These structures are unique because although many people used such systems at the time, Kohala has some of the few to survive. The leeward slopes of Kohala were used for sugar plantations in the late 19th century. The trip from the fields to the mills and then boats was mechanized by steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
in 1883. Several plantations on the mountain were consolidated into the Kohala Sugar Company by 1937. At the peak of its production, the company had 600 employees, 13000 acre (20 sq mi) of land, and a capacity of 45000 t (99,208,018 lb) of raw sugar per year. In 1975 the company finally closed down.
Kohala supports a very complex hydrological cycle
Water cycle
The water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at various places in the water cycle...
. In the early part of the 20th century, this was exploited by building surface irrigational channel
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
s designed to capture water at the higher elevations and distribute it to the then-extensive sugarcane
Sugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...
industry. In 1905, after 18 months and the loss of 17 lives, the Kohala Ditch, a vast network of flumes and ditches, measuring 22 mi (35 km) in length, was completed. Its has since come into use by ranches, farms, and homes. A portion of the ditch became a tourist attraction until it was damaged by the 2006 Hawaii earthquake
2006 Hawaii earthquake
The 2006 Hawaii earthquake was an offshore earthquake occurring southwest from Puakō and north of Kailua-Kona, Hawaii, just offshore of the Kona Airport, on Sunday October 15, 2006 at 7:07:49 AM local time . It measured 6.7 on the moment magnitude scale, and was located at , at a depth of...
, centered just southwest of the mountain.
The Hawaii County Department of Water Supply relies on streams from Kohala to supply water to the population of the island. With increasing demand, the original surface channels have been supplemented by deep wells
Water well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...
designed to channel groundwater for domestic use.
In 2003 the Kohala Watershed Partnership (KWP) was formed, a voluntary group of private land owners and state managers, designed to help manage the Kohala watershed
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
and to protect it from threats, most especially invasive species.
The land around Kohala is administered as two districts, North Kohala and South Kohala, of the County of Hawaii
Hawaii County, Hawaii
Hawaii County is a county located in the U.S. state of Hawaii in the Hawaiian Islands. It is coterminous with the Island of Hawaii, often called the "Big Island" to distinguish it from the state as a whole. As of the 2010 Census the population was 185,079. The county seat is Hilo. There are no...
. The beaches, parks, golf courses, and resorts in South Kohala are called "the Kohala Coast."
King Kamehameha I
Kamehameha I
Kamehameha I , also known as Kamehameha the Great, conquered the Hawaiian Islands and formally established the Kingdom of Hawaii in 1810. By developing alliances with the major Pacific colonial powers, Kamehameha preserved Hawaii's independence under his rule...
, the first King of the unified Hawaiian Islands
Kingdom of Hawaii
The Kingdom of Hawaii was established during the years 1795 to 1810 with the subjugation of the smaller independent chiefdoms of Oahu, Maui, Molokai, Lānai, Kauai and Niihau by the chiefdom of Hawaii into one unified government...
, was born near Upolu Point
Upolu Point
Upolu Point is the most northern point on the island of Hawaii in the Hawaiian Islands. It is an extruding landform created by cooled lava from an old eruption from Kohala volcano. The main town on the extrusion is Hawi, Hawaii about 2 miles inland...
, the northern tip of Kohala. The site is within Kohala Historical Sites State Monument. The original Kamehameha Statue
Kamehameha Statue
Several Kamehameha Statues honor the monarch who founded the Kingdom of Hawaii.-Gould's work:One stands prominently in front of Aliiolani Hale in Honolulu, Hawaii. The statue had its origins in 1878 when Walter M. Gibson, a member of the Hawaiian government at the time, wanted to commemorate the...
stands in front of the community center in Kapaau, and replicas of the statue are found at Aliiōlani Hale
Aliiolani Hale
Aliiōlani Hale is a building located in downtown Honolulu, Hawaii, currently used as the home of the Hawaii State Supreme Court. It is the former seat of government of the Kingdom of Hawaii and the Republic of Hawaii....
in Honolulu, and in the United States Capitol
United States Capitol
The United States Capitol is the meeting place of the United States Congress, the legislature of the federal government of the United States. Located in Washington, D.C., it sits atop Capitol Hill at the eastern end of the National Mall...
at the Hall of Columns
Hall of Columns
The Hall of Columns is a more than hallway lined with twenty-eight fluted columns in the south wing extension of the United States Capitol. It is also the gallery for eighteen statues of the National Statuary Hall Collection.-History:...
in Washington, D.C.