How Do Glaciers Erode Land
21.ane: Glacial Erosion and Deposition
- Folio ID
- 12741
Lesson Objectives
- Discuss the different erosional features formed by tall glaciers.
- Describe the processes by which glaciers change the underlying rocks.
- Discuss the particles deposited by glaciers as they accelerate and recede.
- Describe the landforms created past glacial deposits.
Vocabulary
- tall (valley) glacier
- continental glacier
- end moraine
- glacial erratic
- glacial striations
- glacial till
- glaciers
- ground moraine
- hanging valley
- lateral moraine
- medial moraine
- moraine
- plucking
- last moraine
- varve
Introduction
Glaciers cover about 10% of the land surface near Earth'southward poles and they are as well institute in high mountains. During the Water ice Ages, glaciers covered as much as xxx% of Earth. Around 600 to 800 meg years ago, geologists think that virtually all of the Earth was covered in snowfall and ice. Scientists use the evidence of erosion and deposition left by glaciers to practise a kind of detective work to figure out where the water ice one time was.
Formation and Movement of Glaciers
Glaciers are solid ice that move extremely slowly forth the land surface (Effigy below). Glacial ice erodes and shapes the underlying rocks. Glaciers also deposit sediments in characteristic landforms. The 2 types of glaciers are:
- Continental glaciers are big water ice sheets that cover relatively apartment ground. These glaciers flow outward from where the greatest amount of snow and ice accumulate.
- Alpine or valley glaciers flow downhill through mountains along existing valleys.
A satellite prototype of glaciers in the Himalaya with some features labeled.
Glacial Erosion
Glaciers erode the underlying rock past abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock, the water freezes and pushes pieces of rock outward. The stone is and then plucked out and carried abroad by the flowing ice of the moving glacier (Figure beneath). With the weight of the water ice over them, these rocks tin scratch deeply into the underlying bedrock making long, parallel grooves in the boulder, called glacial striations.
Glacial striations point the direction a glacier has gone.
Mount glaciers leave behind unique erosional features. When a glacier cuts through a 'V' shaped river valley, the glacier pucks rocks from the sides and lesser. This widens the valley and steepens the walls, making a 'U' shaped valley (Figure beneath).
A U shaped valley in Glacier National Park.
Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower 'U' shaped valleys. A hanging valleyforms where the primary glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure below).
Yosemite Valley is known for waterfalls that plunge from hanging valleys.
Upwards loftier on a mountain, where a glacier originates, rocks are pulled abroad from valley walls. Some of the resulting erosional features are shown: Figure below and Figure beneath.
(a) A bowl-shaped cirque in Glacier National Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in dissimilar directions from a mountain acme, leave behind a sharp sided horn, similar the Matterhorn in Switzerland. (d) When glaciers move down reverse sides of a mount, a sharp edged ridge, called an arête, forms between them.
A roche moutonée forms where a glacier smooths the uphill side of the bedrock and plucks away rock from the downslope side.
Depositional Features of Glaciers
Equally glaciers menstruation, mechanical weathering loosens rock on the valley walls, which falls as droppings on the glacier. Glaciers tin can carry rock of any size, from behemothic boulders to silt (Effigy below). These rocks tin can be carried for many kilometers for many years. These rocks with a different rock type or origin from the surrounding bedrock are glacial erratics. Melting glaciers deposit all the large and pocket-sized bits of rocky material they are carrying in a pile. These unsorted deposits of stone are chosen glacial till.
A big boulder dropped by a glacier is a glacial erratic.
Glacial till is found in different types of deposits. Linear stone deposits are chosen moraines. Geologists study moraines to figure out how far glaciers extended and how long it took them to melt away. Moraines are named by their location relative to the glacier:
- Lateral moraines form at the edges of the glacier as material drops onto the glacier from erosion of the valley walls.
- Medial moraines form where the lateral moraines of two tributary glaciers join together in the eye of a larger glacier (Effigy below).
The long, dark lines are medial and lateral moraines.
- Sediment from underneath the glacier becomes a ground moraine later the glacier melts. Basis moraine contributes to the fertile transported soils in many regions.
- Terminal moraines are long ridges of till left at the furthest point the glacier reached.
- Terminate moraines are deposited where the glacier stopped for a long enough menstruation to create a rocky ridge as it retreated. Long Island in New York is formed by ii end moraines.
(a) An esker is a winding ridge of sand and gravel deposited under a glacier by a stream of meltwater. (b) A drumlin is an asymmetrical loma made of sediments that points in the direction the ice moved. Usually drumlins are found in groups called drumlin fields.
While glaciers dump unsorted sediments, glacial meltwater can sort and re-send the sediments (Figure beneath).
(a) A sorted deposit of sand and smaller particles is stratified drift. A broad area of stratified drift from meltwater over broad region is an outwash plain. (b) Kettle lakes course every bit blocks of ice in glacial till melt.
- Effort to option out some of the glacial features seen in this Glacier National Park video:http://www.visitmt.com/national_parks/glacier/video_series/part_3.htm.
Several types of stratified deposits form in glacial regions but are not formed directly by the water ice. Varves grade where lakes are covered by water ice in the winter. Night, fine-grained clays sink to the bottom in winter but melting water ice in spring brings running water that deposits lighter colored sands. Each alternate dark/light layer represents 1 yr of deposits. If during a year, a glacier accumulates more ice than melts away, the glacier advances downhill. If a glacier melts more than information technology accumulates over a year, information technology is retreating (Effigy below).
Grinnell Glacier in Glacier National Park has been retreating over the past 70 years.
Lesson Summary
- The movement of ice in the form of glaciers has transformed our mountainous land surfaces with its tremendous power of erosion.
- U-shaped valleys, hanging valleys, cirques, horns, and aretes are features sculpted by water ice.
- The eroded material is later deposited equally large glacial erratics, in moraines, stratified drift, outwash plains, and drumlins.
- Varves are a very useful yearly eolith that forms in glacial lakes.
Review Questions
- How much of the Earth's land surface is covered by glaciers today? Where are they found?
- What are the 2 types of glaciers and how are they different from each other?
- What is the shape of a valley that has been eroded by rivers? How does a glacier change that shape and what does it become?
- What 2 different features class as smaller side glaciers join the central main glacier?
- How do glaciers erode the surrounding rocks?
- Name the erosional features that are formed past glaciers loftier in the mountains and describe how they course.
- Describe the dissimilar types of moraines formed by glaciers.
- Draw the difference between glacial till and stratified drift. Give an case of how each type of deposit forms.
- Name and describe the two asymmetrical colina shaped landforms created past glaciers.
Points to Consider
- What features would you look for to determine if glaciers had always been nowadays?
- If glaciers had never formed, how would soil in Midwestern North America be different?
- Can the process of erosion produce landforms that are cute?
How Do Glaciers Erode Land,
Source: https://geo.libretexts.org/Courses/Lumen_Learning/Book:_Earth_Science_%28Lumen%29/21:_Glaciers/21.01:_Glacial_Erosion_and_Deposition
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