Glaciology

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.

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]

Glacier.zermatt.arp.750pix
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.
Rothera station 2
Glaciologist Erin Pettit in Antarctica, 2016

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

Bylot Island Glacier (cropped)
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.

  • Alpine – ice flows down the valleys of mountainous areas and forms a tongue of ice moving towards the plains below. Alpine glaciers tend to make the topography more rugged, by adding and improving the scale of existing features such as large ravines called cirques and ridges where the rims of two cirques meet called arêtes.
  • Continental – an ice sheet found today, only in high latitudes (Greenland/Antarctica), thousands of square kilometers in area and thousands of meters thick. These tend to smooth out the landscapes.

Zones of glaciers

  • Accumulation, where the formation of ice is faster than its removal.
  • Wastage or ablation, where the sum of melting, calving and evaporation (sublimation) is greater than the amount of snow added each year.
  • Snow line, the area that marks the transition from the accumulation to the ablation zone and vice versa.

Movement

Khurdopin glacier & Shimshal River
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.[2]
Glaciers of Shimsal Valley from space
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 input of precipitation that exceeds the output, the glacier is advancing. Conversely, if the output from evaporation, sublimation, melting, and calving exceed the glaciers precipitation input the glacier is receding. This is referred to as an interglacial period. During periods where ice 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. During times in which the input of precipitation to the glacier is equivalent to the ice lost from calving, evaporation, and melting of the glacier, there is a steady-state condition. Within the glacier, the ice has a downward movement in the accumulation zone and an upwards movement in the ablation zone.

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.
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.

Rate of movement

Movement of the glacier is very slow. Its velocity varies from a few centimeters per day to a few meters per day. The rate of movement depends upon the numbers of factors which are listed below :

Glacial deposits[3]

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

Stratified

Outwash sand/gravel 
from front of glaciers, found on a plain
Kettles 
block 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 (cropped)
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. ^ Richard S. Williams, Jr. (1987). "Annals of Glaciology, v.9" (PDF). International Glaciological Society. p. 255. Retrieved 7 February 2011.
  2. ^ Khurdopin glacier & Shimshal River, Pakistan
  3. ^ a b Mahapatra, G.B. (1994). Text book of Physical Geology. Nazia printers, Delhi. p. 269. ISBN 81-239-0110-0.

References

  • Benn, Douglas I. and David J. A. Evans. Glaciers and Glaciation. London; Arnold, 1998. ISBN 0-340-58431-9
  • Greve, Ralf and Heinz Blatter. Dynamics of Ice Sheets and Glaciers. Berlin etc.; Springer, 2009. ISBN 978-3-642-03414-5
  • Hambrey, Michael and Jürg Alean. Glaciers. 2nd ed. Cambridge and New York; Cambridge University Press, 2004. ISBN 0-521-82808-2
  • Hooke, Roger LeB. Principles of Glacier Mechanics. 2nd ed. Cambridge and New York; Cambridge University Press, 2005. ISBN 0-521-54416-5
  • Paterson, W. Stanley B. The Physics of Glaciers. 3rd ed. Oxford etc.; Pergamon Press, 1994. ISBN 0-08-037944-3
  • van der Veen, Cornelis J. Fundamentals of Glacier Dynamics. Rotterdam; A. A. Balkema, 1999. ISBN 90-5410-471-6

External links

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.

The amount of snow and ice gained in the accumulation zone and the amount of snow and ice lost in the ablation zone determine glacier mass balance. Often mass balance measurements are made in the ablation zone using snow stakes.

Accumulation zone

On a glacier, the accumulation zone is the area above the firn line, where snowfall accumulates and exceeds the losses from ablation, (melting, evaporation, and sublimation). The annual equilibrium line separates the accumulation and ablation zone annually. The accumulation zone is also defined as the part of a glacier's surface, usually at higher elevations, on which there is net accumulation of snow, which subsequently turns into firn and then glacier ice. Part of the glacier where snow builds up and turns to ice moves outward from there.

Basal sliding

Basal sliding is the act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant. This movement very much depends on the temperature of the area, the slope of the glacier, the bed roughness, the amount of meltwater from the glacier, and the glacier's size.

The movement that happens to these glaciers as they slide is that of a jerky motion where any seismic events, especially at the base of glacier, can cause movement. Most movement is found to be caused by pressured meltwater or very small water-saturated sediments underneath the glacier. This gives the glacier a much smoother surface on which to move as opposed to a harsh surface that tends to slow the speed of the sliding. Although meltwater is the most common source of basal sliding, it has been shown that water-saturated sediment can also play up to 90% of the basal movement these glaciers make.

Most activity seen from basal sliding is within thin glaciers that are resting on a steep slope, and this most commonly happens during the summer seasons when surface meltwater runoff peaks. Factors that can slow or stop basal sliding relate to the glacier's composition and also the surrounding environment. Glacier movement is resisted by debris, whether it is inside the glacier or under the glacier. This can affect the amount of movement that is made by the glacier by a large percentage especially if the slope on which it lies is low. The traction caused by this sediment can halt a steadily moving glacier if it interferes with the underlying sediment or water that was helping to carry it.

The Great Lakes were created due to basal movement.

Crag and tail

A crag (sometimes spelled cragg, or in Scotland craig) is a rocky hill or mountain, generally isolated from other high ground. Crags are formed when a glacier or ice sheet passes over an area that contains a particularly resistant rock formation (often granite, a volcanic plug or some other volcanic structure). The force of the glacier erodes the surrounding softer material, leaving the rocky block protruding from the surrounding terrain. Frequently the crag serves as a partial shelter to softer material in the wake of the glacier, which remains as a gradual fan or ridge forming a tapered ramp (called the tail) up the leeward side of the crag.

In older examples, or those latterly surrounded by the sea, the tail is often missing, having been removed by post-glacial erosion.

Examples of such crag and tail formations include:

The Castle Rock in Edinburgh, Scotland, the rock on which Edinburgh Castle stands

Salisbury Crags and Arthur's Seat

North Berwick Law

Three in or near Stirling, including the rock on which Stirling Castle stands

"Scrabo Hill" in Newtownards, Northern Ireland ( Scrabo Tower stands on the erosion-resistant Crag)

Glacial period

A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The last glacial period ended about 15,000 years ago. The Holocene epoch is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state.

Ice divide

An ice divide is the boundary on an ice sheet, ice cap or glacier separating opposing flow directions of ice, analogous to a water divide. Such ice divides are important for geochronology investigations using ice cores, because such coring is typically made on top of a dome of an ice sheet to avoid interference caused by horizontal ice movement. Ice divides are used for looking at what the atmosphere was like in history. The ice is very accurate because instead of shifting horizontally like normal ice, it moves vertically downward with time trapping gases into its layers. Scientist find these ice divides and take ice cores from them, which are typically long cylinder poles of ice, and evaluate them. Once they have these ice cores, they are able to look through it and find elements that the snow and ice carried down with it during that time period such as sulfate, nitrate, and other ions. These ice cores are important in determining how our atmosphere has changed for the better or worse, and how we can fix it such as the greenhouse effect which discovered when scientist found how much more greenhouse gasses was in our atmosphere than there was in the past.Scientists from around the United States came together to find the perfect ice divide in order to go the furthest into the past. They formed the WAIS project. This project is funded by the United States National Science Foundation, and is run by scientists from many organizations such as National Ice Core Laboratory, Ice Drilling Design and Operations (IDDO), and over fifty Universities. The WAIS project is located in West Antarctica, and the goal is to look into the past 100,000 years. WAIS is better than other ice divides because of the amount of snow it gets. This large amount of snow causes there to be a very small off-set from the ages of the ice to the air and gases trapped inside. This gives the scientists to give much more precise predictions of what the atmosphere was like in history. If the WAIS project is a success it will educate scientists around the world how the atmosphere of Earth has changed completely over 100,000 years.

Ice tongue

An ice tongue is a long and narrow sheet of ice projecting out from the coastline. An ice tongue forms when a valley glacier moves very rapidly out into the ocean or a lake.

Two examples of ice tongues are the Erebus Ice Tongue and the Drygalski Ice Tongue.

Kame delta

A kame delta (or ice-contact delta, morainic delta) is a glacial landform formed by a stream of melt water flowing through or around a glacier and depositing material, known as kame (stratified sequence of sediments) deposits. Upon entering a proglacial lake at the end (terminus) of a glacier, the river/stream deposit these sediments. This landform can be observed after the glacier has melted and the delta's asymmetrical triangular shape is visible. Once the glacier melts, the edges of the delta may subside as ice under it melts. Glacial till is deposited on the lateral sides of the delta, as the glacier melts.

Moraine-dammed lake

A moraine-dammed lake occurs when the terminal moraine has prevented some meltwater from leaving the valley. Its most common shape is that of a long ribbon (ribbon lake).

Example of moraine dammed lakes include:

Argentina/Chile: General Carrera/Buenos Aires Lake

Chile: Calafquén Lake, Panguipulli Lake

New Zealand: Lake Hāwea, Lake Ohau, Lake Pukaki, Lake Tekapo, Lake Wakatipu, and Lake Wanaka (i.e., almost all large lakes in the South Island)

Switzerland: Lake Zurich

United States: Donner Lake in California, Flathead Lake in Montana, Mille Lacs Lake in Minnesota, Wallowa Lake in Oregon

Wales: Llyn Peris and its twin Llyn Padarn.In the 19th century the Argentine explorer Francisco Perito Moreno suggested that many Patagonian lakes draining to the Pacific were in fact part of the Atlantic basin but had been moraine dammed during the quaternary glaciations changing their outlets to the west. He argued that as originally belonging to the Atlantic basin these lakes should be awarded to Argentina. Most of the lakes situated in the Himalaya of Nepal and Bhutan are also of the moraine dammed type. They may burst at any time. That is why the areas below such lakes have high risk of flooding.

Moulin (geomorphology)

A moulin or glacier mill is a roughly circular, vertical to nearly vertical well-like shaft within a glacier or ice sheet which water enters from the surface. The term is derived from the French word for mill.They can be up to 10 meters wide and are typically found on ice sheets and flat areas of a glacier in a region of transverse crevasses. Moulins can reach the bottom of the glacier, hundreds of meters deep, or may only reach the depth of common crevasse formation (about 10–40 m) where the stream flows englacially. They are the most typical cause for the formation of a glacier cave.

Moulins are parts of the internal structure of glaciers, that carry meltwater from the surface down to wherever it may go. Water from a moulin often exits the glacier at base level, sometimes into the sea, and occasionally the lower end of a moulin may be exposed in the face of a glacier or at the edge of a stagnant block of ice.

Water from moulins may help lubricate the base of the glacier, affecting glacial motion. Given an appropriate relationship between an ice sheet and the terrain, the head of water in a moulin can provide the power and medium with which a tunnel valley may be formed. The role of this water in lubricating the base of ice sheets and glaciers is complex and it is implicated in accelerating the speed of glaciers and thus the rate of glacial calving.

Nunatak

A nunatak (from Inuit nunataq) is an exposed, often rocky element of a ridge, mountain, or peak not covered with ice or snow within (or at the edge of) an ice field or glacier. They are also called glacial islands. Examples are natural pyramidal peaks. When rounded by glacial action, smaller rock promontories may be referred to as rognons.The word is of Greenlandic origin and has been used in English since the 1870s.

Pulju moraine

A Pulju moraine (Swedish: Pulju-morän) is a type of moraine found in northern Finland. Pulju moraines were first identified as distinct moraine type in 1967 by Finnish geologist Raimo Kujansuu who noticed moraines that resembled Veiki moraines as those described by Gunnar Hoppe in 1952 but were smaller. Raimo Kujansuu described Pulju moraines with the following words:

...consists of small hummocks, often only from one to five meters high, or of ridges of the same height and between 50 and 300 meters long, which are situated helter-skelter or in thick clusters running either parallel to the movement or margin of the ice sheet or crossvalleywise. In many spots one also meets with ring ridges, measuring no more than 50 to 150 meters in diameter. The slopes are gentle and the hollows between the ridges are mostly filled with peat.

Together with Veiki moraines Pulju moraines form landscapes of the type "ice-walled lake plains".

Randkluft

A randkluft (from the German for marginal cleft/crevasse) or rimaye (from the same French IPA: [ʁimaj]) is the headwall gap between a glacier or snowfield and the adjacent rock face at the back of the cirque or, more loosely, between the rock face and the side of the glacier.

In French, the word rimaye covers both notions of randkluft and bergschrund.

Serac

A serac (originally from Swiss French sérac) is a block or column of glacial ice, often formed by intersecting crevasses on a glacier. Commonly house-sized or larger, they are dangerous to mountaineers, since they may topple with little warning. Even when stabilized by persistent cold weather, they can be an impediment to glacier travel.

Seracs are found within an icefall, often in large numbers, or on ice faces on the lower edge of a hanging glacier. Notable examples of the overhanging glacier edge type are well-known obstacles on some of the world's highest mountains, including K2 at "The Bottleneck" and Kanchenjunga on the border of India and Nepal. Significant seracs in the Alps are found on the northeast face of Piz Roseg, the north face of the Dent d'Hérens, and the north face of Lyskamm.

Sevetti moraine

The Sevetti moraine is a particular assemblage of morainic forms found between Partakko and Sevettijärvi in northern Finland. The Sevetti moraines are disposed in trains about 50 km long and 2–3 km wide. They have rugged surfaces.

Starvation (glaciology)

In glaciology, starvation occurs when a glacier retreats, not because of temperature increases, but due to precipitation so low that the ice flow downward into the zone of ablation exceeds the replenishment from snowfall. Eventually, the ice will move so far down that it either calves into the ocean or melts.

When starvation does occur, however, it can almost always be reversed by slight changes in precipitation, such as are brought about by mountain ranges. Thus, even if glaciers do not cover a lowland due to low precipitation, glaciation is almost certain to occur at higher elevations.

Suncup (snow)

Suncups are bowl-shaped open depressions into a snow surface, normally wider than they are deep. They form closely packed, honeycomb, often hexagonal patterns with sharp narrow ridges separating smoothly concave hollows. For a given set of suncups, the hollows are normally all around the same size, meaning that the pattern is quasi-periodic on 20–80 cm scales. The depressions are typically 2–50 cm deep.Suncups form during the ablation (melting away) of snowy surfaces. It is thought they can form in a number of different ways. These include melting of clean snow by incident solar radiation in bright sunny conditions, but also during melting away of dirty snow under windy or overcast conditions, during which particles in the snow accumulate on the crests between hollows, insulating them.

Till

Till or glacial till is unsorted glacial sediment.

Till is derived from the erosion and entrainment of material by the moving ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.

Till is classified into primary deposits, laid down directly by glaciers, and secondary deposits, reworked by fluvial transport and other processes.

Till plain

A till plain is an extensive flat plain of glacial till that forms when a sheet of ice becomes detached from the main body of a glacier and melts in place, depositing the sediments it carried. Ground moraines are formed when the till melts out of the glacier in irregular heaps, forming rolling hills.

Till plains created by the Wisconsin glaciation cover much of northern Ohio (see Glacial till plains (Ohio)).

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