Glaciation

Glaciation

• An $ice age$ is a period during which large parts of several continents are covered by $ice sheets$. The last ice age to affect Ireland ended roughly $12,000 years ago.$
• During that ice age, the temperatures in the northern hemisphere were so low that snow and ice did not get a chance to melt. Year after year, layers of snow and ice built up until it was compressed or $compacted$ together to form huge $masses$ of ice called $glaciers$
• Glaciers formed in $upland areas$. The effect of $gravity$ eventually moved them $downslope$. Some glaciers melted while others joined together to form ice sheets. These $ice sheets$ covered huge areas of land.

What causes an ice age?

We have already learned that the Earth is constantly hanging because of $plate tectonics$. These changes, along with other factors can bring about changes in $global temperatures$. We do not know for sure why ice ages occur, but some factors that might be important in causing an ice age include.

• %%Earth's orbit and axis:%% The Earth's $orbit$ around the sun changes regularly from oval or $elliptical$, to $circular$. The Earth is tilted on its $axis$, and the $angle$ of its tilt is always changing. These changes happen over $tens of thousands of years$ and it is thought that they have an important influence on The Earth's climate.
• %%Earth's atmosphere%%: When there is less $carbon dioxide$ (CO) in the atmosphere to trap the sun's heat, global temperatures can drop.
• %%Ocean currents%%: Ocean currents $distribute heat$. When they change course, $ice sheets$ build up.

Glacial erosion

Plucking

As a glacier moves, there is $friction$ between the $glacier$ and the $ground$ beneath it. This $friction$ causes the $bottom$ of the $glacier$ to $melt$. The $meltwater$ makes its way into $cracks in the rocks$ underneath the glacier. The meltwater then $refreezes$ around the rocks.

When the glacier moves, it $plucks$ the $frozen meltwater$ and the rocks from the ground. The rocks are then carried away with the glacier.

Abrasion

As the glacier moves, the rocks attached to it $scratch$ and $scrape$ the $surface rock$ underneath and $on the sides$ of the $valley$. The scratch marks left behind on rocks are called $striations$ (stree-at-ions). These marks tell us the $direction$ in which the glacier moved.

Cirques

A cirque is a $basin-shaped hollow$ in a mountain. It looks like an armchair. It has $three steep sides$ and often contains a lake. A cirque was the birthplace of a glacier

%%Formation:%%

• A cirque is formed when snow $accumulates$ (builds up) in a hollow high up on a mountain. The snow is $compressed$ to form ice.
• The ice $plucks$ rocks from the sides of the mountain as it begins to move. These rocks make the hollow $deeper$ through the process of $abrasion.$
• The ice eventually $overflows$ from the hollow and $gravity$ causes the ice to move downhill.
• The ice that is left behind melts and forms a lake in the hollow. This lake is called a tarn

%%Examples of cirques:%%

• $Devil’s Punchbowl$ - Co. Kerry
• $Barley lake$ - Co. Cork

Aretes

A pyramidal peak is a $steep-sided peak$ between three or more cirques

%%Formation:%%

When $three$ or more cirques form around a mountain top, a steep-sided peak remains between them

%%Examples of pyramidal peaks%%:

• Comeragh Mountains - Co. Waterford
• Matterhorn - Switzerland

U-shaped valley

A glaciated or U-shaped valley has a $wide, flat floor$ and $steep sides$

%%Formation:%%

• When a glacier moves out of a cirque and down the mountain, it follows the easiest $route$ possible
• This route is often a $V-shaped valley$ that has previously been carved out by a river
• The glacier uses $plucking$ and $abrasion$ to widen and deepen the valley. This changes it from a V-shaped valley to a $U-shaped valley.$
• As the glacier moves through the valley, it also cuts off the tips off the $interlocking spurs$ created by the river, leaving behind $truncated spurs$

%%Examples of U-shaped valleys:%%

• Glendalough - Co. Wicklow
• Gap of Dunloe - Co. Kerry
• \

Deposition

How glaciers transport their load

Glaces $carry$ large amounts of material from upland areas, where they are formed, to lowland areas carry this $load$ in the following ways:

• Material is pushed $in front$ of the glacier like a sweeping brush
• Material is carried $on top$ of the glacier Materials rolled along at the $sides$ of the glacier and $underneath$ the ice
• Material falls through cracks or $crevasses$ in the glacier, and so is carried $within$ it.

  Glaciers gather and lose material along the way. The material that is $transported$ by the glacier and la $deposited$ by it is called a $moraine$.

Boulder clay plains

A boulder clay plain is a $lowland area$ that is covered in a layer of boulders, clay, sand and stones called $boulder clay.$

%%Formation:%%

• As the glacier melts, it $deposits$ its load of eroded material consisting of $boulders,$ $clay$, $sand$ and $stones$.
• Boulder clay is very $fertile$ and excellent for agriculture.

%%Example of boulder clay plains%%:

• The Golden Vale - Munster

Drumlins

Drumlins are $oval-shaped hills$ made of $boulder clay$

%%Formation:%%

• A drumlin forms when a glacier deposits mounds of boulder clay.
• The glacier then continues its journey and smooths the boulder clay as it moves over it.
• The steep slope or stoss end of the drumlin hows us what direction the glacier was coming from The gentle slope or lee slope shows us what direction the glacier was travelling in.
• Drumlins usually occur in clusters, forming what is called a basket of eggs landscape

%%Examples of drumlins:%% Claw Bay in Co. Mayo and Strangford Lough in Co. Down

Erratics

Erratics are $large boulders$ that were $transported$ from their original location by a glacier and then $deposited$ in an area where the $rock type$ is different.

For example, there are boulders of $granite$ in the $Burren,$ Co. Clare, where the local rock type is $limestone$. The nearest source of granite is north Galway, which tells us that the ice sheet that passed over the Burren came from the north.

Moraines

A moraine is the name given to the material transported and later $deposited$ on the $valley floor$ by a glacier

%%Formation:%%

• As a glacier through a valley it $drops off$ some of the material that it has eroded from the upper slopes at either $side$ of the glacier This deposit is known as a $lateral moraine$. It is a $ridge$ at the $sides$ of the valley.
• When two glaciers $meet$, the lateral moraines of each glacier and meet, creating a $medial moraine$
• Materials also moved along and deposited $underneath$ a glacier. This is called the $ground$ $moraine$
• Finally when a glacier $stops$ moving, a ridge, made up of the material that it was pushing $in front$ of it, deposited. This material is called a $terminal moraine$. It tells us where the moraine ended
• Other ridges of deposited materials are found behind the terminal moraine and are called $end moraines$

Landforms of fluvio-glacial deposition

Eskers

An esker is a long, narrow ridge of sand and gravel that winds its way along a lowland landscape.

Formation:

• When a glacier begins to melt, streams of meltwater

  carrying a load of eroded material flow through a tunnel that is carved out under the glacier.

• When the load becomes too great, some material is

deposited on the bed of the meltwater stream.

• The stream loses its energy when it exits the tunnel and it deposits the remainder of its load. This forms a ridge of sand and gravel on the surrounding plain.
• This ridge is known as an esker. Roads have been built on eskers in many areas as they provide good foundations.

Example of an esker: Esker Riada in Co. Galway.

Outwash planes

A outwash plane is a low flat area of land made of sand + gravel found at the front of a terminal moraine

Formation:

• As the glacier melts, meltwater carrying a load of sand and gravel flows from the front of the glacier and spreads out over the lowland area.
• As the meltwater loses energy, it begins to deposit the heavier material first, followed by the lighter material.

Example of an outwash plain: The Curragh in Co Kildare.

People and glaciation

Benefits

Agriculture

• Boulderclay deposited by glacier => fertile soil
• Example: Golden Vale in Munster

Tourism

• Glacial landscapes => tourist attractions
• Lakes in glacial areas => recreational purposes   * Boating   * Fishing
• Example: Gap of Dunloe Co Kerry or Barley Lake Co Cork

HEP

• Glacial lakes => natural reservoir for HEP stations
• Example: Turlough Hill Co. Wicklow

Roads

• Glaciated U-Shaped valleys provide natural routeways
• Example: Gap of Dunloe Co. Kerry
• Eskers provdide naturalroad foundations

Industry

• Sand + gravel from eskers used in construction industry
• Glacial lakes => water supplies

Negatives

Poor agricultural land in upland areas

• Glaciers remove soil cover in upland areas => unsuitable for agriculture
• Sheep farming only option

Poor drainage

• Glacial deposits => drumlins => poor drainage => bogs

Flooding

• Glaciers => melt => sea levels rise
• Lowland costal areas => risk of flooding

\