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.

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

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.

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 topography more rugged by adding and improving the scale of existing features. Various features include large ravines called cirques and arêtes, which are ridges where the rims of two cirques meet.
  • 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.
  • Ablation (or wastage) – when 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 glacial accumulation to the ablation zone and vice versa.

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.[2]
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.
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.

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]
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
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. 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
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