Ubinas
Encyclopedia
Ubinas is Peru
's most recently active volcano. Until 2006, this stratovolcano
had not erupted for about 40 years.
. The upper slopes of the volcano
, composed primarily of Pleistocene
andesitic lava flows, steepen to nearly 45 degrees. The steep-walled, 1.4 km wide and 150 m deep summit caldera
contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank of Ubinas extend 10 km from the volcano.
The volcano is a composite cone built on a high plateau formed from Oligo-Miocene ignimbrites and intrusive rocks of upper Tertiary
age. Ubinas comprises two edifices that divide two major periods of its eruptive behaviour. The first is the lower volcano under 600 m high called Ubinas 1 (eruptive period >376 ka), which collapsed and formed a debris-avalanche deposit as far as 12 km downstream Rio Ubinas. This collapse was followed by an eruption of non-welded ignimbrites, ponding to a thickness of 150 m over 5 km from the summit, and in turn was covered by a 100 m thick ash/pumice
deposit. Ubinas 1 is overlain by a steeper cone more than 900 m high called Ubinas 2 (eruptive period <376 ka). Ubinas 2 formed the summit caldera, with walls up to 300 m high that consist of hydrothermally altered lava
flows and floored by a 20 m thick pile of lapilli
and ash-fall layer. This morphology
was created by frequent eruptions in the Late Holocene
from the younger inner crater. The inner crater Figure 5.5 is under 200 m high and shows pervasive hydrothermal alteration and abundant fractures. Countless explosive events have taken place inside the summit caldera during the last 9.7 ky, and it has been suggested by Thouret et al. that the caldera be considered gravitationally unstable.
and therefore a greater source of fertile mantle
material. Some volcanologists believe that this variation in dip angle along the Nazca Lines
is responsible for activity in the Andean volcanic zones and the areas of inactivity in between them.
-fall deposit which achieved a thickness of 25 cm over 40 km from the summit. Smaller eruptions since have also shown a wide range in composition from mafic
to rhyolitic, which may indicate that magma mixing is occurring in the feeding magma chamber.
On April 23, 2006, Peru declared a state of emergency
in towns near the volcano.
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
's most recently active volcano. Until 2006, this stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
had not erupted for about 40 years.
Description
Ubinas is located in southwestern PeruPeru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
. The upper slopes of the volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
, composed primarily of 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 ....
andesitic lava flows, steepen to nearly 45 degrees. The steep-walled, 1.4 km wide and 150 m deep 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...
contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank of Ubinas extend 10 km from the volcano.
The volcano is a composite cone built on a high plateau formed from Oligo-Miocene ignimbrites and intrusive rocks of upper Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
age. Ubinas comprises two edifices that divide two major periods of its eruptive behaviour. The first is the lower volcano under 600 m high called Ubinas 1 (eruptive period >376 ka), which collapsed and formed a debris-avalanche deposit as far as 12 km downstream Rio Ubinas. This collapse was followed by an eruption of non-welded ignimbrites, ponding to a thickness of 150 m over 5 km from the summit, and in turn was covered by a 100 m thick ash/pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
deposit. Ubinas 1 is overlain by a steeper cone more than 900 m high called Ubinas 2 (eruptive period <376 ka). Ubinas 2 formed the summit caldera, with walls up to 300 m high that consist of hydrothermally altered lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
flows and floored by a 20 m thick pile of lapilli
Lapilli
Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli means "little stones" in Latin. They are in some senses similar to ooids or pisoids in calcareous sediments.By definition lapilli range...
and ash-fall layer. This morphology
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...
was created by frequent eruptions in the Late Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
from the younger inner crater. The inner crater Figure 5.5 is under 200 m high and shows pervasive hydrothermal alteration and abundant fractures. Countless explosive events have taken place inside the summit caldera during the last 9.7 ky, and it has been suggested by Thouret et al. that the caldera be considered gravitationally unstable.
Geologic setting
Ubinas is located 230 km east of the Peru-Chile trench and about 150 km above the Benioff-Wadati plane, where the Nazca plate is subducting at a dip ranging from 20 – 30˚ as characteristic of the CVZ. The steep dip angle of the subducting plate can correspond to a thicker wedge of asthenosphereAsthenosphere
The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...
and therefore a greater source of fertile mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
material. Some volcanologists believe that this variation in dip angle along the Nazca Lines
Nazca Lines
The Nazca Lines are a series of ancient geoglyphs located in the Nazca Desert in southern Peru. They were designated a UNESCO World Heritage Site in 1994. The high, arid plateau stretches more than between the towns of Nazca and Palpa on the Pampas de Jumana about 400 km south of Lima...
is responsible for activity in the Andean volcanic zones and the areas of inactivity in between them.
History
There are at least two Plinian deposits, reflective of explosive eruptions with more differentiated magmas. The latest such eruption occurred between 1000 and 1160 A.D., producing an andesitic pumicePumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
-fall deposit which achieved a thickness of 25 cm over 40 km from the summit. Smaller eruptions since have also shown a wide range in composition from mafic
Mafic
Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
to rhyolitic, which may indicate that magma mixing is occurring in the feeding magma chamber.
Activity update
As of April 22, 2006, the volcano is erupting with fumaroles and ash plumes.On April 23, 2006, Peru declared a state of emergency
State of emergency
A state of emergency is a governmental declaration that may suspend some normal functions of the executive, legislative and judicial powers, alert citizens to change their normal behaviours, or order government agencies to implement emergency preparedness plans. It can also be used as a rationale...
in towns near the volcano.