Glaciology

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Lateral moraine on a glacier joining the Gorner Glacier, Zermatt, Swiss Alps. The moraine is the high bank of debris in the top left hand quarter of the image. Glacier.zermatt.arp.750pix.jpg
Lateral moraine on a glacier joining the Gorner Glacier, Zermatt, Swiss Alps. The moraine is the high bank of debris in the top left hand quarter of the image.
Glaciologist Erin Pettit in Antarctica, 2016 Rothera station 2.jpg
Glaciologist Erin Pettit in Antarctica, 2016

Glaciology (from Latin: glacies , "frost, ice", and Ancient Greek: λόγος, logos , "subject matter"; literally "study of ice") is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice.

Contents

Glaciology is an interdisciplinary Earth science that integrates geophysics, geology, physical geography, geomorphology, climatology, meteorology, hydrology, biology, and ecology. The impact of glaciers on people includes the fields of human geography and anthropology. The discoveries of water ice on the Moon, Mars, Europa and Pluto add an extraterrestrial component to the field, which is referred to as "astroglaciology". [1]

Overview

A glacier is an extended mass of ice formed from snow falling and accumulating over a long period of time; glaciers move very slowly, either descending from high mountains, as in valley glaciers, or moving outward from centers of accumulation, as in continental glaciers.

Areas of study within glaciology include glacial history and the reconstruction of past glaciation. A glaciologist is a person who studies glaciers. A glacial geologist studies glacial deposits and glacial erosive features on the landscape. Glaciology and glacial geology are key areas of polar research.

Types

A Bylot Island glacier, Sirmilik National Park, Nunavut. This mountain glacier is one of many coming down from the interior ice cap on top of the Byam Martin Mountains. Bylot Island Glacier (cropped).jpg
A Bylot Island glacier, Sirmilik National Park, Nunavut. This mountain glacier is one of many coming down from the interior ice cap on top of the Byam Martin Mountains.

Glaciers can be identified by their geometry and the relationship to the surrounding topography. There are two general categories of glaciation which glaciologists distinguish: alpine glaciation, accumulations or "rivers of ice" confined to valleys; and continental glaciation, unrestricted accumulations which once covered much of the northern continents.

Zones of glaciers

Glacier equilibrium line and ELA

The glacier equilibrium line is the line separating the glacial accumulation area above from the ablation area below. The equilibrium line altitude (ELA) and its change over the years is a key indicator of the health of a glacier. A longterm monitoring of the ELA may be used as indication to climate change.

Movement

Khurdopin glacier and Shimshal River, Gilgit-Baltistan, northern Pakistan 2017. Several glaciers flow into the Shimshal Valley, and are prone to blocking the river. Khurdopin glacier surged in 2016-17, creating a sizable lake. Khurdopin glacier & Shimshal River.jpg
Khurdopin glacier and Shimshal River, Gilgit-Baltistan, northern Pakistan 2017. Several glaciers flow into the Shimshal Valley, and are prone to blocking the river. Khurdopin glacier surged in 2016–17, creating a sizable lake.
Glaciers of Shimsal Valley from space, May 13, 2017. Khurdopin glacier has dammed the Shimshal River, forming a glacial lake. The river has started to carve a path through the toe of the glacier. By early August 2017, the lake had completely drained. Glaciers of Shimsal Valley from space.jpg
Glaciers of Shimsal Valley from space, May 13, 2017. Khurdopin glacier has dammed the Shimshal River, forming a glacial lake. The river has started to carve a path through the toe of the glacier. By early August 2017, the lake had completely drained.

When a glacier is experiencing an accumulation input by precipitation (snow or refreezing rain) that exceeds the output by ablation, the glacier shows a positive glacier mass balance and will advance. Conversely, if the loss of volume (from evaporation, sublimation, melting, and calving) exceeds the accumulation, the glacier shows a negative glacier mass balance and the glacier will melt back. During times in which the volume input to the glacier by precipitation is equivalent to the ice volume lost from calving, evaporation, and melting, the glacier has a steady-state condition.

Some glaciers show periods where the glacier is advancing at an extreme rate, that is typically 100 times faster than what is considered normal, it is referred to as a surging glacier. Surge periods may occur at an interval of 10 to 15 years, e.g. on Svalbard. This is caused mainly due to a long lasting accumulation period on subpolar glaciers frozen to the ground in the accumulation area. When the stress due to the additional volume in the accumulation area increases, the pressure melting point of the ice at its base may be reached, the basal glacier ice will melt and the glacier will surge on a film of meltwater.

Rate of movement

The movement of glaciers is usually slow. Its velocity varies from a few centimeters to a few meters per day. The rate of movement depends upon the factors listed below:

Glacial Terminology

Ablation
Wastage of the glacier through sublimation, ice melting and iceberg calving.
Ablation zone
Area of a glacier in which the annual loss of ice through ablation exceeds the annual gain from precipitation.
Arête
An acute ridge of rock where two cirques meet.
Bergschrund
Crevasse formed near the head of a glacier, where the mass of ice has rotated, sheared and torn itself apart in the manner of a geological fault.
Cirque, Corrie or cwm
Bowl shaped depression excavated by the source of a glacier.
Creep
Adjustment to stress at a molecular level.
Flow
Movement (of ice) in a constant direction.
Fracture
Brittle failure (breaking of ice) under the stress raised when movement is too rapid to be accommodated by creep. It happens for example, as the central part of a glacier moves faster than the edges.
Moraine
Accumulated debris that has been carried by a glacier and deposited at its sides (lateral moraine) or at its foot (terminal moraine).
Névé
Area at the top of a glacier (often a cirque) where snow accumulates and feeds the glacier.
Horn
Spire of rock, also known as a pyramidal peak, formed by the headward erosion of three or more cirques around a single mountain. It is an extreme case of an arête.
Plucking/Quarrying
Where the adhesion of the ice to the rock is stronger than the cohesion of the rock, part of the rock leaves with the flowing ice.
Tarn
A post-glacial lake in a cirque.
Tunnel valley
The tunnel that is formed by hydraulic erosion of ice and rock below an ice sheet margin. The tunnel valley is what remains of it in the underlying rock when the ice sheet has melted.

Glacial deposits [3]

A kettle pond in Hossa, Suomussalmi municipality, Finland Kettle pond Hossa.jpg
A kettle pond in Hossa, Suomussalmi municipality, Finland

Stratified

Outwash sand/gravel
From front of glaciers, found on a plain.
Kettles
When a lock of stagnant ice leaves a depression or pit.
Eskers
Steep sided ridges of gravel/sand, possibly caused by streams running under stagnant ice.
Kames
Stratified drift builds up low steep hills.
Varves
Alternating thin sedimentary beds (coarse and fine) of a proglacial lake. Summer conditions deposit more and coarser material and those of the winter, less and finer.

Unstratified

Drowned drumlin in Clew Bay, Ireland Drowned drumlin in Clew Bay (cropped).jpg
Drowned drumlin in Clew Bay, Ireland
Till-unsorted
(Glacial flour to boulders) deposited by receding/advancing glaciers, forming moraines, and drumlins.
Moraines
(Terminal) material deposited at the end; (Ground) material deposited as glacier melts; (lateral) material deposited along the sides.
Drumlins
Smooth elongated hills composed of till.
Ribbed moraines
Large subglacial elongated hills transverse to former ice flow.

See also

Notes

  1. Williams, Richard S. (1987). "Summary Remarks". Annals of Glaciology. 9: 254–255. doi: 10.3189/S0260305500000987 .
  2. Khurdopin glacier & Shimshal River, Pakistan
  3. 1 2 Mahapatra, G.B. (1994). Text book of Physical Geology. Nazia printers, Delhi. p. 269. ISBN   81-239-0110-0.

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, moraines, or fjords. 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.

Moraine Glacially formed accumulation of unconsolidated debris

A moraine is any accumulation of unconsolidated debris, sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sheet. It may consist of partly rounded particles ranging in size from boulders down to gravel and sand, in a groundmass of finely-divided clayey material sometimes called glacial flour. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines and medial moraines.

Till Unsorted glacial sediment

Till or glacial till is unsorted glacial sediment.

Cryosphere Those portions of Earths surface where water is in solid form

The cryosphere is an all-encompassing term for those portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground. Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in the global climate and in climate model response to global changes. The term deglaciation describes the retreat of cryospheric features. Cryology is the study of cryospheres.

Wisconsin glaciation North American glacial ice sheet

The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide Ice Sheet, which covered the high latitudes of central and eastern North America. This advance was synchronous with global glaciation during the last glacial period, including the North American alpine glacier advance, known as the Pinedale glaciation. The Wisconsin glaciation extended from approximately 75,000 to 11,000 years ago, between the Sangamonian Stage and the current interglacial, the Holocene. The maximum ice extent occurred approximately 25,000–21,000 years ago during the last glacial maximum, also known as the Late Wisconsin in North America.

Ice sheet Large mass of glacial ice

In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are in Antarctica and Greenland; during the last glacial period at Last Glacial Maximum (LGM) the Laurentide Ice Sheet covered much of North America, the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America.

Last Glacial Period Period of major glaciations of the northern hemisphere (115,000–12,000 years ago)

The Last Glacial Period (LGP) occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The definition of the Quaternary as beginning 2.58 million years ago (Mya) is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya, in the mid-Cenozoic. The term Late Cenozoic Ice Age is used to include this early phase.

Cirque An amphitheatre-like valley formed by glacial erosion

A cirque is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie and cwm. A cirque may also be a similarly shaped landform arising from fluvial erosion.

Dirt cone Depositional glacial feature of ice or snow with an insulating layer of dirt

A dirt cone is a type of depositional glacial feature. Dirt cones are not actually made entirely of dirt. They have a core of ice, snow, or firn that gets covered with material and insulated. The material, if it is thick enough, will protect the underlying core from ablation. The thickness of material needed to insulate the core is called the “critical thickness.” If the material is less thick than the critical thickness, it will actually speed up erosion of the core through ablation. This is called “indirect ablation.” The cone would then begin melting and shrinking away.

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.

Terminal moraine

A terminal moraine, also called end moraine, is a type of moraine that forms at the terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed by the front edge of the ice, is driven no further and instead is deposited in an unsorted pile of sediment. Because the glacier acts very much like a conveyor belt, the longer it stays in one place, the greater the amount of material that will be deposited. The moraine is left as the marking point of the terminal extent of the ice.

Glacier mass balance

Crucial to the survival of a glacier is its mass balance or surface mass balance (SMB), the difference between accumulation and ablation. Climate change may cause variations in both temperature and snowfall, causing changes in the surface mass balance. Changes in mass balance control a glacier's long-term behavior and are the most sensitive climate indicators on a glacier. From 1980 to 2012 the mean cumulative mass loss of glaciers reporting mass balance to the World Glacier Monitoring Service is −16 m. This includes 23 consecutive years of negative mass balances.

Glacier ice accumulation

Glacier ice accumulation occurs through accumulation of snow and other frozen precipitation, as well as through other means including rime ice, avalanching from hanging glaciers on cliffs and mountainsides above, and re-freezing of glacier meltwater as superimposed ice. Accumulation is one element in the glacier mass balance formula, with ablation counteracting. With successive years in which accumulation exceeds ablation, then a glacier will experience positive mass balance, and its terminus will advance.

Ablation zone

Ablation zone or ablation area refers to the low-altitude area of a glacier or ice sheet below firn with a net loss in ice mass due to melting, sublimation, evaporation, ice calving, aeolian processes like blowing snow, avalanche, and any other ablation. The equilibrium line altitude (ELA) or snow line separates the ablation zone from the higher-altitude accumulation zone. The ablation zone often contains meltwater features such as supraglacial lakes, englacial streams, and subglacial lakes. Sediments dropped in the ablation zone forming small mounds or hillocks are called kames. Kame and kettle hole topography is useful in identifying an ablation zone of a glacier. The seasonally melting glacier deposits much sediment at its fringes in the ablation area. Ablation constitutes a key part of the glacier mass balance.

Glacier morphology

Glacier morphology, or the form a glacier takes, is influenced by temperature, precipitation, topography, and other factors. The goal of glacial morphology is to gain a better understanding of glaciated landscapes, and the way they are shaped. Types of glaciers can range from massive ice sheets, such as the Greenland ice sheet, to small cirque glaciers found perched on mountain tops. Glaciers can be grouped into two main categories:

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.

Fluvioglacial landforms are those that result from the associated erosion and deposition of sediments caused by glacial meltwater. These landforms may also be referred to as glaciofluvial in nature. Glaciers contain suspended sediment loads, much of which is initially picked up from the underlying landmass. Landforms are shaped by glacial erosion through processes such as glacial quarrying, abrasion, and meltwater. Glacial meltwater contributes to the erosion of bedrock through both mechanical and chemical processes.

Deglaciation describes the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice sheet or frozen surface layer, and the resulting exposure of the Earth's surface. The decline of the cryosphere due to ablation can occur on any scale from global to localized to a particular glacier. After the Last Glacial Maximum, the last deglaciation begun, which lasted until the early Holocene. Around much of Earth, deglaciation during the last 100 years has been accelerating as a result of climate change, partly brought on by anthropogenic changes to greenhouse gases.

Brenva Glacier

The Brenva Glacier is a valley glacier, located on the southern side of the Mont Blanc massif in the Alps. It is the second longest and eighth largest glacier in Italy, and descends down into Val Veny, close to Entrèves, near Courmayeur. Over the centuries it has experienced a number of major rock avalanches which have shaped the glacier and influenced its movement.

Glacier head Top of a glacier

A glacier head is the top of a glacier. Although glaciers seem motionless to the observer they are in constant motion and the terminus is always either advancing or retreating.

References