Geology of Connecticut
Encyclopedia
As part of New England
, Connecticut
has undergone much geologic change shaped by plate tectonics
, volcanism
, and glacial activity.
, the super-continent Pangea was formed as the Iapetus Ocean
closed up and the proto-North American continent collided with Avalonia
, part of modern-day Africa
. This caused great uplift and the creation of the Appalachian Mountains
, which, at the time, were bigger than modern-day Himalayas
. Erosion of the Appalachian Mountains
now exposes metamorphic rocks once very deep in the Earth’s mantle
and uplifted during this time period.
floor started spreading and great extensional forces were experienced, resulting in faulting
. Connecticut’s famous Eastern Border Fault was created, a fault which begins in New Haven
and stretches 130 miles up to Keene, New Hampshire
. As a result, the land west of this fault was downset, creating a rift valley
and causing the land to tilt an average of 15 to 25 degrees. The fault is currently inactive. The formation of this basin eventually refilled with soft fluvial and alluvial sediments.
s, glacial activity shaped much of New England
’s landscape, eroding mountains, leaving glacial till scattered everywhere, and forming glacial lakes. At its greatest extent, one of these glaciers leaves behind a moraine
which becomes today's Long Island
. One of the biggest glacial lakes of the time was Glacial Lake Hitchcock
. It formed when the Laurentide ice sheet
retreated and glacial meltwater began to accumulate at the glacier’s terminal moraine
in Rocky Hill, Connecticut
and back up into the Connecticut River
. The glacial lake left behind a soft, varve
d landscape, gathering silt
and sand in the summertime due to the influx of glacial meltwater and clay in the wintertime as the lake froze until it was later drained.
, resedimented and oft flooded by the Connecticut River
, making it a very soft, nutrient-replenished area and host to the majority of Connecticut’s farmland soils. The land on either side of the Connecticut River Valley is less suitable for farmlands. The eastern section holds the shallow Proto-North American Terrane
while the western section contains the Iapetos and Avalonian Terrane
s, which still holds remnants of glacial till and lack the soft fluvial
sediments so prominent in the Connecticut River Valley region.
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
, Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...
has undergone much geologic change shaped by plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
, and glacial activity.
Appalachian Mountains
During the early TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, the super-continent Pangea was formed as the Iapetus Ocean
Iapetus Ocean
The Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
closed up and the proto-North American continent collided with Avalonia
Avalonia
Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, and the eastern coast of North America. It is the source of many of the older rocks of Western Europe, Atlantic Canada, and parts of the coastal United States...
, part of modern-day Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. This caused great uplift and the creation of the Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
, which, at the time, were bigger than modern-day Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
. Erosion of the Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
now exposes metamorphic rocks once very deep in the Earth’s 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....
and uplifted during this time period.
Eastern Border Fault
About 200 million years after this collision and the formation of Pangea, during the middle of the Mesozoic Era, the Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
floor started spreading and great extensional forces were experienced, resulting in faulting
Geologic fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of tectonic forces...
. Connecticut’s famous Eastern Border Fault was created, a fault which begins in New Haven
New Haven, Connecticut
New Haven is the second-largest city in Connecticut and the sixth-largest in New England. According to the 2010 Census, New Haven's population increased by 5.0% between 2000 and 2010, a rate higher than that of the State of Connecticut, and higher than that of the state's five largest cities, and...
and stretches 130 miles up to Keene, New Hampshire
Keene, New Hampshire
Keene is a city in Cheshire County, New Hampshire, United States. The population was 23,409 at the 2010 census. It is the county seat of Cheshire County.Keene is home to Keene State College and Antioch University New England, and hosts the annual Pumpkin Fest...
. As a result, the land west of this fault was downset, creating a rift valley
Rift valley
A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift or fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion...
and causing the land to tilt an average of 15 to 25 degrees. The fault is currently inactive. The formation of this basin eventually refilled with soft fluvial and alluvial sediments.
Ice Age
During Ice AgeIce age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
s, glacial activity shaped much of New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
’s landscape, eroding mountains, leaving glacial till scattered everywhere, and forming glacial lakes. At its greatest extent, one of these glaciers leaves behind a moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
which becomes today's Long Island
Long Island
Long Island is an island located in the southeast part of the U.S. state of New York, just east of Manhattan. Stretching northeast into the Atlantic Ocean, Long Island contains four counties, two of which are boroughs of New York City , and two of which are mainly suburban...
. One of the biggest glacial lakes of the time was Glacial Lake Hitchcock
Lake Hitchcock
Lake Hitchcock was a glacial lake that formed approximately 15,000 years ago in the late Pleistocene epoch. After the Laurentide ice sheet retreated, glacial ice melt accumulated at the terminal moraine and blocked up the Connecticut River, creating the long, narrow lake...
. It formed when the Laurentide ice sheet
Laurentide ice sheet
The Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles, including most of Canada and a large portion of the northern United States, multiple times during Quaternary glacial epochs. It last covered most of northern North America between c. 95,000 and...
retreated and glacial meltwater began to accumulate at the glacier’s terminal moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
in Rocky Hill, Connecticut
Rocky Hill, Connecticut
Rocky Hill is a town in Hartford County, Connecticut, United States. The population was 17,966 at the 2000 census. Rocky Hill was part of Wethersfield, the neighboring town to the north, until it was independently incorporated in 1849....
and back up into the Connecticut River
Connecticut River
The Connecticut River is the largest and longest river in New England, and also an American Heritage River. It flows roughly south, starting from the Fourth Connecticut Lake in New Hampshire. After flowing through the remaining Connecticut Lakes and Lake Francis, it defines the border between the...
. The glacial lake left behind a soft, varve
Varve
A varve is an annual layer of sediment or sedimentary rock.The word 'varve' is derived from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as Hvarfig lera on the first map produced by the Geological Survey of Sweden in...
d landscape, gathering silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
and sand in the summertime due to the influx of glacial meltwater and clay in the wintertime as the lake froze until it was later drained.
River Valley
This soft surface has since been downcutDowncutting
Downcutting, also called erosional downcutting or downward erosion or vertical erosion is a geological process that deepens the channel of a stream or valley by removing material from the stream's bed or the valley's floor. How fast downcutting occurs depends on the stream's base level, which is...
, resedimented and oft flooded by the Connecticut River
Connecticut River
The Connecticut River is the largest and longest river in New England, and also an American Heritage River. It flows roughly south, starting from the Fourth Connecticut Lake in New Hampshire. After flowing through the remaining Connecticut Lakes and Lake Francis, it defines the border between the...
, making it a very soft, nutrient-replenished area and host to the majority of Connecticut’s farmland soils. The land on either side of the Connecticut River Valley is less suitable for farmlands. The eastern section holds the shallow Proto-North American Terrane
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
while the western section contains the Iapetos and Avalonian Terrane
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
s, which still holds remnants of glacial till and lack the soft fluvial
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
sediments so prominent in the Connecticut River Valley region.
