Glacial lake

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The Seven Rila Lakes in Rila mountain, Bulgaria, are of glacial origin. Rila 7 lakes circus panorama edit1.jpg
The Seven Rila Lakes in Rila mountain, Bulgaria, are of glacial origin.
The Great Lakes as seen from space. The Great Lakes are the largest glacial lakes in the world. Great Lakes from space.jpg
The Great Lakes as seen from space. The Great Lakes are the largest glacial lakes in the world.
The prehistoric glacial lake Agassiz once held more water than contained by all lakes in the world today. Agassiz.jpg
The prehistoric glacial lake Agassiz once held more water than contained by all lakes in the world today.

A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land, and then melts, filling the depression created by the glacier. [1]

Contents

Formation

Near the end of the last glacial period, roughly 10,000 years ago, glaciers began to retreat. [2] A retreating glacier often left behind large deposits of ice in hollows between drumlins or hills. As the ice age ended, these melted to create lakes. This is apparent in the Lake District in Northwestern England where post-glacial sediments are normally between 4 and 6 meters deep. [2] These lakes are often surrounded by drumlins, along with other evidence of the glacier such as moraines, eskers and erosional features such as striations and chatter marks.

These lakes are clearly visible in aerial photos of landforms in regions that were glaciated during the last ice age. The coastlines near these areas are typically very irregular, reflecting the same geological process.[ citation needed ]

By contrast, other areas have fewer lakes that often appear attached to rivers. Their coastlines are smoother. These areas were carved more by water erosion.

The formation and characteristics of glacial lakes vary between location and can be classified into glacial erosion lake, ice-blocked lake, moraine-dammed lake, other glacial lake, supraglacial lake, and subglacial lake. [1]

Glacial lakes and changing climate

Since the glaciation of the Little Ice Age, Earth has lost more than 50% of its glaciers. This along with the current increase in retreating glaciers caused by climate change has created a shift from frozen to liquid water, increasing the extent and volume of glacial lakes around the world. Most glacial lakes present today can be found in Asia, Europe, and North America. The area which will see the greatest increase in lake formation is the Southern Tibetan Plateau region from debris covered glaciers. [3] This increase in glacial lake formation also indicates an increase in occurrence of glacial lake outburst flood events caused by damming and subsequent breaking of moraine and ice.

Sediments

The amount of sediment found in glacial lakes varies from four to six meters in depth, and has a general stratigraphic sequence of; organic muds, glacial clays, silty clays, and sands based on time of formation. [4]

Over time the glacial lake sediments are subjected to change. As seen in the English Lake District, the layers of the sediments at the bottom of the lakes contain evidence of the rate of erosion. The elemental make up of the sediments are not associated with the lakes themselves, but by the migration of the elements within the soil, such as iron and manganese.

The distribution of these elements, within the lake bed, are attributed to the condition of the drainage basin and the chemical composition of the water.

Sediment deposition can also be influenced by animal activity; including the distribution of biochemical elements, which are elements that are found in organic organisms, such as phosphorus and sulfur.

The amount of halogens and boron found in the sediments accompanies a change in erosional activity. The rate of deposition reflects the amount of halogen and boron in the deposited sediments. [2]

The scouring action of the glaciers pulverizes minerals in the rock over which the glacier passes. These pulverized minerals become sediment at the bottom of the lake, and some of the rock flour becomes suspended in the water column. These suspended minerals support a large population of algae, making the water appear green. [5]

Biotic ecosystem

Seal at Jokulsarlon glacial lagoon in Iceland. A Seal at the Glacial Lagoon.jpg
Seal at Jökulsárlón glacial lagoon in Iceland.

Biodiversity and productivity tend to be lower in glacial lakes as only cold-tolerant and cold-adapted species can withstand their harsh conditions. Glacial rock flour and low nutrient levels create an oligotrophic environment where few species of plankton, fish and benthic organisms reside. [6]

Before becoming a lake the first stages of glacial recession melt enough freshwater to form a shallow lagoon. In the case of Iceland's Jökulsárlón glacial lagoon located on the edge of the Atlantic Ocean, tides bring in an array of fish species to the edge of the glacier. These fish attract an abundance of predators from birds to marine mammals, that are searching for food. These predators include fauna such as, seals, arctic terns and arctic skua. [7]

Glacial lakes that have been formed for a long period of time have a more diverse ecosystem of fauna originating form neighboring tributaries or other glacial refugia. For example, many native species of the great lakes basin entered via the Mississippi basin refugia within the past 14,000 years. [8]

Societal perspectives

Argentino glacial lake at the base of Perito Moreno glacier in Argentina. Perito moreno.jpg
Argentino glacial lake at the base of Perito Moreno glacier in Argentina.

Glacial lakes act as fresh water storage for the replenishing of a regions water supply and serve as potential electricity producers from hydropower.

Glacial lakes' aesthetic nature also stimulates economic activity through the attraction of the tourism industry. [9] Thousands of tourists visit the Jökulsárlón glacial lagoon in Iceland annually to take part in commercial boat tours and every two to four years thousands visit the Argentino glacial lake in Argentina to witness the collapse of the cyclically formed arch of ice from the Perito Moreno glacier, making it one of the largest travel destinations in Patagonia. [10] [11]

See also

Related Research Articles

Glacier Persistent body of ice that is moving under its own weight

A glacier is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow under stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that forms on the surface of bodies of water.

Valley Low area between hills, often with a river running through it

A valley is a low area between hills or mountains typically with a river running through it. In geology, a valley or dale is a depression that is longer than it is wide. The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, at least with respect to the cross section of the slopes or hillsides.

Drumlin Elongated hill formed by the action of glacial ice on the substrate

A drumlin, from the Irish word droimnín, first recorded in 1833, in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine. Clusters of drumlins create a landscape which is often described as having a 'basket of eggs topography'.

Moraine Glacially formed accumulation of unconsolidated debris

A moraine is any glacially formed accumulation of unconsolidated glacial debris that occurs in both currently and formerly glaciated regions on Earth, through geomorphological processes. Moraines are formed from debris previously carried along by a glacier, and normally consist of somewhat rounded particles ranging in size from large boulders to minute glacial flour. Lateral moraines are formed at the side of the ice flow and terminal moraines at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines and medial moraines.

Jökulsárlón

Jökulsárlón is a large glacial lake in southern part of Vatnajökull National Park, Iceland. Situated at the head of the Breiðamerkurjökull glacier, it developed into a lake after the glacier started receding from the edge of the Atlantic Ocean. The lake has grown since then at varying rates because of melting of the glaciers. It is now 1.5 km (0.93 mi) away from the ocean's edge and covers an area of about 18 km2 (6.9 sq mi). In 2009 it was reported to be the deepest lake in Iceland, at over 284 m (932 ft), as glacial retreat extended its boundaries. The size of the lake has increased fourfold since the 1970s.

Jökulhlaup Type of glacial outburst flood

A jökulhlaup is a type of glacial outburst flood. It is an Icelandic term that has been adopted in glaciological terminology in many languages. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland, which are triggered by geothermal heating and occasionally by a volcanic subglacial eruption, but it is now used to describe any large and abrupt release of water from a subglacial or proglacial lake/reservoir.

Glacial erratic

A glacial erratic is glacially-deposited rock differing from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, and are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock in Alberta.

Outwash plain Plain formed from glacier sediment that was transported by meltwater.

An outwash plain, also called a sandur, sandr or sandar, is a plain formed of glacial sediments deposited by meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and carries the debris along. The meltwater at the snout of the glacier deposits its load of sediment over the outwash plain, with larger boulders being deposited near the terminal moraine, and smaller particles travelling further before being deposited. Sandurs are common in Iceland where geothermal activity accelerates the melting of ice flows and the deposition of sediment by meltwater.

Glacial landform Landform created by the action of glaciers

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

Subglacial lake A lake under a glacier

A subglacial lake is a lake that is found under a glacier, typically beneath an ice cap or ice sheet. Subglacial lakes form at the boundary between ice and the underlying bedrock, where gravitational pressure decreases the pressure melting point of ice. Over time, the overlying ice gradually melts at a rate of a few millimeters per year. Meltwater flows from regions of high to low hydraulic pressure under the ice and pools, creating a body of liquid water that can be isolated from the external environment for millions of years.

Depression (geology) Landform sunken or depressed below the surrounding area

In geology, a depression is a landform sunken or depressed below the surrounding area. Depressions form by various mechanisms.

Outwash fan A fan-shaped body of sediments deposited by braided streams from a melting glacier

An outwash fan is a fan-shaped body of sediments deposited by braided streams from a melting glacier. Sediment locked within the ice of the glacier, gets transported by the streams of meltwater, and deposits on the outwash plain, at the terminus of the glacier. The outwash, the sediment transported and deposited by the meltwater and that makes up the fan, is usually poorly sorted due to the short distance traveled before being deposited.

Glacial lake outburst flood A type of outburst flood that occurs when the dam containing a glacial lake fails

A glacial lake outburst flood (GLOF) is a type of outburst flood that occurs when the dam containing a glacial lake fails. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a Jökulhlaup. The dam can consist of glacier ice or a terminal moraine. Failure can happen due to erosion, a buildup of water pressure, an avalanche of rock or heavy snow, an earthquake or cryoseism, volcanic eruptions under the ice, or massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.

Tunnel valley A U-shaped valley originally cut by water under the glacial ice near the margin of continental ice sheets

A tunnel valley is a U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages. They can be as long as 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep.

U-shaped valley Valleys formed by glacial scouring

U-shaped valleys, trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. They have a characteristic U shape, with steep, straight sides and a flat or rounded bottom. Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice, called glacial till or glacial erratic.

Rogen moraine Landform of ridges deposited by a glacier or ice sheet transverse to ice flow

A Rogen moraine is a subglacially formed type of moraine landform, that mainly occurs in Fennoscandia, Scotland, Ireland and Canada. It is one of the three main types of hummocky moraines. They cover large areas that have been covered by ice, and occur mostly in what is believed to have been the central areas of the ice sheets. Rogen moraines are named after Lake Rogen in Härjedalen, Sweden, the landform's type locality. Rogen Nature Reserve serves to protect the unusual area.

Withrow Moraine and Jameson Lake Drumlin Field

The Withrow Moraine and Jameson Lake Drumlin Field is a National Park Service–designated privately owned National Natural Landmark located in Douglas County, Washington state, United States. Withrow Moraine is the only Ice Age terminal moraine on the Waterville Plateau section of the Columbia Plateau. The drumlin field includes excellent examples of glacially-formed elongated hills.

Glacial history of Minnesota

The glacial history of Minnesota is most defined since the onset of the last glacial period, which ended some 10,000 years ago. Within the last million years, most of the Midwestern United States and much of Canada were covered at one time or another with an ice sheet. This continental glacier had a profound effect on the surface features of the area over which it moved. Vast quantities of rock and soil were scraped from the glacial centers to its margins by slowly moving ice and redeposited as drift or till. Much of this drift was dumped into old preglacial river valleys, while some of it was heaped into belts of hills at the margin of the glacier. The chief result of glaciation has been the modification of the preglacial topography by the deposition of drift over the countryside. However, continental glaciers possess great power of erosion and may actually modify the preglacial land surface by scouring and abrading rather than by the deposition of the drift.

Overdeepening Characteristic of basins and valleys eroded by glaciers

Overdeepening is a characteristic of basins and valleys eroded by glaciers. An overdeepened valley profile is often eroded to depths which are hundreds of metres below the deepest continuous line along a valley or watercourse. This phenomenon is observed under modern day glaciers, in salt-water fjords and fresh-water lakes remaining after glaciers melt, as well as in tunnel valleys which are partially or totally filled with sediment. When the channel produced by a glacier is filled with debris, the subsurface geomorphic structure is found to be erosionally cut into bedrock and subsequently filled by sediments. These overdeepened cuts into bedrock structures can reach a depth of several hundred metres below the valley floor.

References

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