Lake Origins - Limnology Exam 2

What percent of all lakes are formed from glacial origin?

74%

What percent of all lakes are formed by tectonic activity?

5%

What is the Pleistocene epoch?

the most recent episode of glaciation, also known as the ice age.

What is a glacier?

An extensive perennial mass of ice which moves over land

Where do glaciers occur?

areas where accumulation of snow/ice occur for many years.

Glacial Scouring

Created by the scraping/gouging action of large, heavy, glaciers.

The Laurentian North American Great Lakes (Canada and USA) were formed by…

1. glacial erosion in deepened/widened valleys

2. the subsequent deposition of moraine

3. gradual uprising of land after the massive weight of the ice disappeared. 

What was the main force that created basins of North American Great Lakes?

glacial scouring

What was a secondary force that created basins of North American Great Lakes?

moraine deposition

what is the tertiary force that created basins of North American Great Lakes?

the gradual uprising of the land after the massive weight of the ice disappeared 

When did the formatin of the great lakes begin?

14,000 years ago by scouring of preexisting river valleys

Where did the great lakes start to drain?

into the St. Lawrence River valley

What are today’s great lakes?

A series of 5 lakes;

1. lake superior 

2. lake Michigan-Huron

3. Lake Erie

4. Lake Ontario 

How are the great lakes connected?

to the Atlantic Ocean by the St. Lawrence River

What is an Ice-margin/ Proglacial lake

The formation of a lake when land in front of the ice margin slopes toward the ice, allowing meltwater to pond directly in contact with the ice. (they form at glacier edges)

What are proglacial lakes most associated with?

the Greenland icecap and antarctica 

what is Lake Agassiz?

A glacial lake that was larger in area than all of the great lakes combined.

The largest body of freshwater to have ever existed in North America

What is a subglacial lake?

it forms beneath a glacier in a basin created by glacial scouring and is permanently covered by a glacial ice.

How are subglacial lakes kept liquid?

1. overlying ice that acts as a thermal insulator

2. water percolating through crevices in a glacier 

3. pressure exerted on lake by weight of glacier

4. geothermal heat

what is Lake Vostok?

A famously large subglacial lake that is estimated to be 15 million years old. Ice core samples have been taken here and found microbial DNA, unknown bacterium, 255 known bacteria, and other historical data.

How are Cirque Lakes formed?

by erosive action of alpine glaciers in the upper end of mountain valleys. The bowl shaped depression is caused by the freezing/thawing of water/ice in rocky concavity just below the headwall.

Cirque Lake characteristics 

typically have a concave basin that meets a nearly vertical headwall above and is bounded below by a lip of rock/moraine. 

what is a moraine lake?

Glacial lakes formed by impoundment (ponding)

How are moraine lakes formed?

When glaciers began to retreat, they deposited rocks/sediment into valleys. The build up of this sediment caused a blockage and formed a barrier for the flowing water and in turn created these types of lakes. 

what is the sediment called that causes the formation of moraine lakes?

Glacial Tillw

what does glacial till consist of?

clay, sand, gravel, cobble, and boulders.

what are moraines?

piles of glacial till deposited by glaciers

what is an Alluvial Dam?

When two rivers join, the faster river dumps sediments at the mouth of the slower river and can eventually block it up and form a type of lake.

What is an Alluvial Dam Lake?

This lake is formed by an ____ fan deposition of glacial sediment that forms a barrier creating a lake. This lake is formed by a combination of glacial and fluvial activity. 

What is an example of an Alluvial Dam Lake?

Lake Pepin (WI)

How is a Kettle Lake formed?

When Glacial till covers/surrounds a patch of ice left behind by a receding glacier, or by depressions made by large blocks of ice broken off from a glacier.

when the ice block melts, it leaves behind a depression in the crust. This depression collects water and forms a lake.

Basic characteristics of Kettle Lakes

typically round with steep sides 

What are the different kinds of Glacial Lakes?

1. proglacial

2. subglacial

3. cirque

4. moraine

5. alluvial dam

6. kettle lake

What are tectonic lakes?

lakes formed in depressions created by movements of tectonic plates.

what are the different kinds of tectonic lakes?

1. grabens

2. uplift lakes

3. earthquake lakes

what is a Graben?

a trench-like depression formed by faulting processes.

when a fault block drops between two parallel faults.

what are the characteristics of a Graben lake?

flat-bottomed, steep-walled, very deep.

how are uplift lakes formed?

by the slow uplifting of the earth’s surface by moderate geological activity.

How are earthquake lakes formed?

when an ___ alters the earth’s surface in such a manner that it facilitates the formation of a lake. Causing damming or depressions.

What is a half graben?

a geologic structure that is bounded by a fault along only one side of its boundaries.

What kind of lake is the oldest and deepest lake in the world? (lake baikal, russia)

Graben (25 myo, 1700 meters deep)

What are the types of volcanic lakes?

1. Volcanic Craters

2. Caldera

3. Maar

4. lava-depression lakes

5. lava-dam lakes/  coulee lakes

What is a Caldera?

Large, cauldron-shaped depression resulting from the explosion or collapse of the enter of a volcano.

Large volcanic craters that form by two different methods.w

what are the two different methods of Caldera formation?

1. explosive

2. collapse

what is the explosive method in the formation of a Caldera?

an explosive volcanic eruption

what is the collapse method in the formation of a caldera?

collapse of surface rock into an empty magma chamber 

What is a Maar?

a volcanic crater that forms when magma contacts ground water to produce steam explosion. 

What is a lava-depression lake?

lakes formed in lava depressions when flowing lava cools and forms depressions in which water is collected

what is a coulee lake?

formed when flowing lava cools and forms blockages or dams. water collects behind the walls of lava to form a lentic body of water.

what are the types of fluvatile/riverine lakes?

1. Leevee lakes

2. oxbow lakes

3. evorsion lakes

What is a Levee lake?

lakes that occur in floodplain river ecosystems. formed when a river floods and carries large particulates over the existing delta walls to form levees outside the main channel walls. “water blocked by the levees to form bodies of water outside of main channel”

what are oxbow lakes?

they are created/subundant in floodplain river ecosystems. they are formed by meandering streams that erode to the point of a loop separating from the main channel and sediment builds up to close the previous opening/connection.

what is an evorsion lake?

they are formed when a waterfall erodes the substrate at the base of the water fall to form a basin.

what is a Karst lake?

when rainwater/ groundwater gradually dissolves bedrock creating underground cavity/cavern alone fissures/fractures. The roof of the underground fracture eventually collapses and creates a sinkhole.

what substrate are Karst lakes/sinkholes common in?

limestone and dolomite

what is a salt-collapse basin?

salt- collapse basins are formed when an underlying layer of salt is dissolved and collapses, forming  a depression in the earth. this depression fills with water and forms a lake

what is a piping lake?

“false karst” lake

They are formed in depressions caused by geological piping that results in turbulent subsurface drainage channels in insoluble rock.

what is piping?

subsurface form of erosion which involves removal of subsurface soil/rock in pipe-like erosion channels; this commonly occurs in highly erodible soil/rock.

what is an aeolian lake?

a lake formed by wind activity, often found in arid or semi-arid regions.

what is a deflation basin?

wind erosion moves sand out of an area creating a depression. these basins are usually shallow, saline, and are seasonal.

what is a playa?

a flat, closed basin that holds water occasionally. usually occupied by shallow water only after periods of prolonged heavy precipitation. 

What are wallows?

bodies of water formed by the activity of larger land herbivores.