Glaciation - The Work of Moving Ice - Chapter 12

Climate

Weather conditions in an area measured over 30 years

Glaciers

Great rivers of ice

Ice Age

About 2M years ago, the climates of countries such as Ireland became much colder. Year after year, snow fell. It began to gather in upland areas, gradually turning into solid ice. The ice slowly began to move to lowland areas under the influence of gravity as great rivers of ice known as glaciers. Some glaciers melted, while others joined together to form ice sheets. The ice sheets covered huge areas of the earth’s surface. An ice age had arrived

Interglacial periods

Warmer periods during the Ice Age. The average length of an interglacial period is 100,000 years.

Processes of Glacial Erosion : Plucking

As ice moves, it causes friction between the ice and the ground below. This friction creates heat, which causes the ice at the base to melt. The meltwater flows into the cracks of the rocks below. The water then refreezes around the rock and sticks to the glacier. When the ice moves forward, it can pull or pluck chunks of rocks out of the ground

Processes of Glacial Erosion : Abrasion

Plucked rocks become embedded in the base of the glacier. As the glacier moves the rocks abrade (scrape and smooth) the surface over which they pass

Features of glacial erosion : Glaciated valley

This is a V-shaped valley which has been straightened and flattened by the movement of a large glacier to become a U-shaped valley

Features of glacial erosion : Cirque

Also knwon as a corrie, this is a large hollow on the side of a mountain. It has three steep sides and is the birthplace of a glacier

Features of glacial erosion :Tarn

This is a lake inside the cirque

Features of glacial erosion : Pyramidal peak

This is a steep-sided pyramid-shaped mountain that was eroded on all sides by many cirques.

Features of glacial erosion : Arete

This is a narrow, steep sided ridge, usually between two cirques

Features of glacial erosion : Paternoster lakes

When a long, narrow lake occupies the floor of a glaciated valley, it is called a ribbon lake. When a few ribbon lakes are linked, they are called paternoster lakes.

Features of glacial erosion : Truncated spur

This was originally an interlocking spur that was eroded, having its ‘head’ cut off as the glacier moved through the valley.

Features of glacial erosion : Hanging valley

This is a small tributary valley that hangs above the main glaciated valley.

U-Shaped glaciated valley

A U-shaped glaciated valley was originally a V-shaped river valley. It became straightened and deepened by a glacier filling it, which changed it to look more U-shaped;

Formation of U-shaped valley

During an ice age a glacier fills a river valley

The base of the glacier melts into the underlying rocks due to the heat caused by friction as the glacier moves. Then the meltwater refreezes, and as the glacier moves on, it plucks chunks of rock out of the ground

Plucked rocks become embedded in the base of the glacier. As the glacier moves, the rocks abrade the rock surface they pass over.

The river’s once V-shaped valley has now been re-shaped into a U-shaped valley

e.g Glendalough, Co. Wicklow, Doolough Valley, Co. Mayo

Fjords

A fjord is a U-shaped valley found under the sea. They were formed when the glacier retreated after carving out a U-shaped valley. As the sea level rose, the U-shaped valley ended up underwater

e.g Killary Harbour, Co. Mayo

Formation of Cirques (Corries)

Snow collects in a mountain hollow high up in the mountain. With repeated snowfalls, the snow compacts to form ice. A glacier is born.

Through plucking and abrasion, the hollow grows deeper. Freeze-thaw action is also at work here.

When the glacier is big enough, it begins to flow over the edge of the cirque. It then begins its journey.

When the glacier melts, a lake called a tarn may be trapped in the cirque hollow

When two cirques form back to back, the ridge between them is known as an arete.

e.g Devil’s Punch Bowl, Co. Kerry

Supraglacial transport

These are materials found on the surface of the glacier, along the top or sides. These materials are carried along as the glacier moves. This material usually has fallen down the mountain and landed on the sides or top of the glacier.

Englacial transport

This is any regolith trapped within the ice, including material that has fallen down cracks in the ice

Subglacial transport

This is any loose regolith trapped underneath the glacier and dragged along the bottom of the ice

Drumlin

Oval-shaped hills that are made of deposited boulder clay (a mixture of sand and clay). They often occur in large numbers known as swarms

 Formation of Erratic

A large boulder deposited by a glacier, in an area where the rock type is different. Because of this, the boulders look out of place in the landscape in which they now stand. Erratics can tell us how far and in which direction the ice has travelled in

e.g Limestone area of the Burren, Co. Clare

Esker

A long narrow ridge of sand or gravel

Outwash plain

A low, flat area composed of sand and gravel deposits found in front of the terminal moraine

Moraine

A mass of rocks and other materials carried down and deposited by a glacier

Recessional Moraine

A moraine marking a temporary stop in the retreat (moving back) of a glacier

Lateral Moraine

Found at the side of a glacier. It is made of broken rock and soil that fell down the mountain and gathered at the side. This is supraglacial material.

Terminal Moraine

Found at the front of the glacier. It is made of material that is pushed ahead of the glacier. A terminal moraine makrs the end point of the glacierM

Medial moraine

Found in the middle of a glacier when two glaciers combine. Their two lateral moraines join together. This is englacial material

Formation of Drumlins

Glacial ice deposits boulder clay in irregular heaps

The ice retreats and then advances again. This time it shapes and smooths the boulder clay into rounded oval-shaped hills

The steep slope of the drumlin is the direction from which the ice advanced. The gentle slope points to the direction in which the ice was travelling. 

e.g Clew Bay, Co. Mayo

Features of glacial meltwater

At the end of an ice age, when global temperatures began to rise and glaciers started to melt, the meltwater flowed out from the melting ice sheet and deposited material across the land surface. The heaviest material, such as stones or gravel, was dropped first, then the lighter material, such as sand and silt

Formation of Esker

As the ice melts, large tunnels of meltwater flow in tunnels beneath the ice. 

When a river leaves an ice tunnel, it slows down immediately and deposits material at the mouth of the tunnel

As the ice slowly melts back, the deposited material is dropped in the form of a long, narrow ridge of sand and gravel

e.g Trim esker system, Co. Meath

Formation of Outwash Plain

As the ice sheet melts, huge amounts of meltwater flow out of it

The water flushes large quantities of sand and gravel onto the lowland beyond the front of the ice

As the meltwater loses energy, it deposits the heaviest material first, followed by the lighter material.

e.g The Curragh, Co. Kildare

How People Interact with and use the wicklow landscpae

Glendalough is a glacial valley in Co. Wicklow. During the last ice age, the valley was carved out by the ice into the U-shaped valley we see today. The area is visited by large amounts of tourists throughout the year

Environmental Impact

Glacial lakes have provided natural resevoirs used for generating hydro-electric power in Co. Wicklow. Hydroelectric energy is a form of renewable energy created by the power of moving water.

Turlough Hill is the central control point for all hydroelectricity generation throughout Ireland. During the highest electricity demand periods, water is released from an upper resevoir and flows through 4 turbines into lower Lough Nahanagan - a tarn lake

Social Impact

The Wicklow Mountains National Park, of which Glendalough is a part of, covers an area of 20,000 hectares, making up much of upland Wicklow. It attracts over 1M visitors every year

There are many walking trails of varying difficulty and distance across Glendalough. Within the valley itself, there are nine color-coded walking trails

Lakes found in the Glendalough Valley - created as a result of ice thaw after the last ice age - attract anglers. The valley is also home to a variety of flora and fauna.

Economic Impact

County Wicklow is known as the Garden of Ireland. The steep topography, created by glaciation makes certain types of farming difficult. Glaciers also removed much of the rich soil cover in upland areas, leaving them highly unsuitable for highly productiove agriculture

Almost 22% of its land area is devoted to forestry, making it one of the most important land uses in the county. A government grant scheme encourages farmers to plant trees, especially on poorer quality land. Forestry also provides employment, both directly and indirectly, for many local people