Glaciers and Glaciation: A Comprehensive and Essential Resource for Glaciology Students and Enthusiasts
Glaciers and Glaciation: A Comprehensive Guide to the Frozen World
Glaciers are among the most fascinating and spectacular natural phenomena on Earth. They cover about 10% of the land surface and store about 75% of the freshwater. They have shaped the landscape, influenced the climate, and affected human history for millions of years. They are also sensitive indicators of environmental change and important sources of water, energy, and tourism.
glaciers and glaciation, 2nd edition benn, douglas | evans, david j a||
But what are glaciers exactly? How do they form and grow? How do they interact with other natural systems? How do they move and deform? How do they shape the landscape and leave behind evidence? These are some of the questions that this article will try to answer, based on the latest scientific knowledge and insights from the classic textbook Glaciers and Glaciation, 2nd edition, by Douglas Benn and David J A Evans. This article will provide a comprehensive overview of the nature, origin, behaviour, and legacy of glaciers and glaciation, as well as some examples and illustrations from different regions of the world.
What are glaciers and how do they form?
The definition and types of glaciers
A glacier is a mass of ice that forms on land by the accumulation and compaction of snow, and that flows under its own weight. Glaciers can be classified into different types based on their size, shape, location, thermal regime, or dynamics. Some of the main types of glaciers are:
Ice sheets: These are the largest glaciers that cover vast areas of land, such as Antarctica and Greenland. They can be thousands of meters thick and contain most of the ice on Earth.
Ice caps: These are smaller than ice sheets but still cover large areas of land, usually in high latitudes or altitudes. They can be dome-shaped or plateau-like, such as those in Iceland or Svalbard.
Ice fields: These are similar to ice caps but have a more irregular shape and are influenced by the underlying topography. They can cover mountain ranges or valleys, such as those in Patagonia or Alaska.
Valley glaciers: These are elongated glaciers that flow along valleys, usually originating from ice caps or ice fields. They can be tens to hundreds of kilometers long and have a U-shaped cross-section, such as those in the Alps or Himalayas.
Cirque glaciers: These are small glaciers that occupy bowl-shaped depressions on mountain slopes, usually forming at the headwaters of valley glaciers. They can be a few kilometers wide and have a circular or oval shape, such as those in the Rocky Mountains or the Andes.
Tidewater glaciers: These are valley glaciers that reach the sea and terminate in ice cliffs, where they calve icebergs. They can be influenced by tides, currents, and waves, and can undergo rapid changes, such as those in Greenland or Antarctica.
Outlet glaciers: These are glaciers that drain ice from ice sheets or ice caps through narrow channels or fjords. They can be similar to tidewater glaciers but may also end on land, such as those in Antarctica or Iceland.
Piedmont glaciers: These are glaciers that spread out at the base of a mountain range or at the edge of an ice sheet or ice cap. They can have a fan-shaped or lobate appearance, such as those in Alaska or New Zealand.
Ice shelves: These are extensions of ice sheets or outlet glaciers that float on the ocean. They can be hundreds of kilometers wide and tens of meters thick, and can calve large icebergs, such as those in Antarctica or Canada.
The process of glacier formation and growth
Glaciers form and grow by the accumulation and compaction of snow over time. Snow is a form of precipitation that consists of ice crystals that fall from clouds. Snow can have different shapes and sizes depending on the temperature and humidity of the air. Snow that falls on the ground can undergo various changes depending on the weather conditions and the season. Some of the main processes that affect snow are:
Sublimation: This is the direct conversion of snow into water vapor without melting. It can occur when the air is dry and the temperature is low, causing snow to lose mass and density.
Melting: This is the conversion of snow into liquid water by absorbing heat from the air or the sun. It can occur when the temperature is above freezing, causing snow to lose mass and volume.
Refreezing: This is the conversion of liquid water into ice by releasing heat to the air or the ground. It can occur when the temperature is below freezing, causing snow to gain mass and volume.
Settling: This is the downward movement of snow due to gravity and pressure. It can occur when snow accumulates on the ground, causing snow to lose air and increase density.
Metamorphism: This is the change in shape and size of snow crystals due to temperature gradients, pressure, and water vapor. It can occur when snow undergoes sublimation, melting, refreezing, or settling, causing snow to become more rounded and compact.
The process of glacier formation and growth involves a series of stages that transform snow into glacier ice. The stages are:
Fresh snow: This is newly fallen snow that has a low density (about 50-100 kg/m) and a high air content (about 90-95%). It consists of irregular and fragile ice crystals that reflect light and give snow a white color.
Firn: This is aged snow that has survived at least one summer melt season. It has a higher density (about 300-500 kg/m) and a lower air content (about 50-70%). It consists of rounded and bonded ice grains that transmit light and give firn a translucent appearance.
Glacier ice: This is mature firn that has been buried under more snow for several years. It has a very high density (about 800-900 kg/m) and a very low air content (about 10-20%). It consists of large and interlocking ice crystals that absorb light and give glacier ice a blue color.
The process of glacier formation and growth depends on the balance between accumulation and ablation. Accumulation is the addition of mass to a glacier by snowfall, avalanches, wind drift, or refreezing of meltwater. Ablation is the loss of mass from a glacier by melting, sublimation, calving, or erosion. The difference between accumulation and ablation is called the mass balance, which determines whether a glacier is advancing, retreating, or stable.
The factors that influence glacier distribution and size
The distribution and size of glaciers on Earth are influenced by various factors that affect the availability of snow and the rate of ablation. Some of the main factors are:
The landforms and sediments created by glaciers
Glaciers create various landforms and sediments by their erosional and depositional actions. Some of these landforms and sediments are:
Glacial moraines: These are accumulations of unsorted and unstratified rocks and sediments that are deposited at the margins or along the surface of glaciers. Glacial moraines can be classified into different types based on their location and shape, such as lateral moraines, medial moraines, terminal moraines, recessional moraines, or ground moraines.
Eskers: These are long and narrow ridges of stratified sand and gravel that are deposited by meltwater streams flowing under or within glaciers. Eskers can be several kilometers long and tens of meters high, and often have a winding or sinuous shape.
Kames: These are mounds or hills of stratified sand and gravel that are deposited by meltwater streams flowing on top of or near the terminus of glaciers. Kames can be a few meters to a few hundred meters high, and often have a conical or irregular shape.
Drumlins: These are elongated hills of glacial till that are streamlined by the flow of glaciers. Drumlins can be a few meters to a few hundred meters high, and have a blunt end facing upstream and a tapered end facing downstream.
Ribbed moraines: These are parallel ridges of glacial till that are formed by the deformation of subglacial sediments. Ribbed moraines can be a few meters to tens of meters high, and have a transverse or longitudinal orientation relative to ice flow.
Outwash plains: These are flat or gently sloping areas of stratified sand and gravel that are deposited by meltwater streams flowing away from the terminus of glaciers. Outwash plains can cover large areas and have a braided or anastomosing drainage pattern.
Glacial erratics: These are large boulders or rocks that are transported and deposited by glaciers far away from their source area. Glacial erratics can have a different lithology or size than the surrounding rocks, and can indicate the direction and distance of ice movement.
Till: This is a general term for unsorted and unstratified rocks and sediments that are deposited directly by glacier ice. Till can vary in texture, composition, and thickness depending on the source material, transport distance, and depositional environment.
Conclusion
Glaciers are fascinating natural phenomena that have shaped the Earth's surface for millions of years. They form by the accumulation and compaction of snow over time, and move under their own weight by internal deformation and basal sliding. They interact with climate and other natural systems by storing and releasing water in different forms and at different rates. They also create various features and phenomena on the surface or at the base of glaciers by eroding and depositing rocks and sediments as they move over land. Glaciers are sensitive indicators of environmental change and important sources of water, energy, and tourism. However, they are also threatened by global warming, which is causing them to melt faster than they can accumulate snow. The loss of glaciers will have profound consequences for the Earth's hydrological cycle, climate system, landscape evolution, and biodiversity.
FAQs
What is the difference between glacier ice and snow?: Glacier ice is snow that has been compressed and metamorphosed into a dense, grainy ice with a low air content. Snow is a form of precipitation that consists of ice crystals with a high air content.
What is the difference between glacier ice and sea ice?: Glacier ice is freshwater ice that forms on land by the accumulation and compaction of snow. Sea ice is saltwater ice that forms on the ocean by the freezing of seawater.
What is the difference between alpine glaciers and ice sheets?: Alpine glaciers are rivers of ice that flow along valleys in mountainous regions. Ice sheets are pancakelike masses of ice that cover large areas of land, such as Antarctica and Greenland.
What is the difference between glacial erosion and glacial deposition?: Glacial erosion is the removal of material from the bedrock or the surface by glaciers. Glacial deposition is the addition of material to the bedrock or the surface by glaciers.
What is the difference between glacial till and glacial outwash?: Glacial till is unsorted and unstratified rocks and sediments that are deposited directly by glacier ice. Glacial outwash is stratified sand and gravel that are deposited by meltwater streams flowing away from glaciers.
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