The Last Ice Age (Leaving Cert Geography): Revision Notes
The Last Ice Age
Introduction to ice ages
Currently, around 10% of Earth's land surface is covered by glaciers, which are mainly found near the North and South Poles. However, throughout Earth's long history, there have been multiple periods when glaciers covered entire continents. These extended cold periods are known as ice ages.
When glaciers advance across landscapes, they significantly modify the terrain through both erosional and depositional processes, fundamentally changing the shape and characteristics of the land.
Glacial processes are incredibly powerful forces that can carve out entire valleys, create lakes, and transport massive amounts of rock and sediment across continents. The landscapes we see today in many northern regions are direct results of these glacial activities.
The Pleistocene period
The most recent ice age started approximately 2.6 million years ago and finished around 10,000 years ago. This geological period is known as the Pleistocene.
Pleistocene: The geological era spanning from 1.6 million years ago to 10,000 years ago, characterised by repeated glacial and interglacial periods.
During the Pleistocene, massive ice sheets covered Greenland, Antarctica, Northern Europe, and North America. This era was marked by significant temperature fluctuations, with periods of warming and cooling occurring repeatedly. Scientists have identified at least five distinct periods of glacial advance, separated by warmer interglacial periods.
The concept of Earth experiencing ice ages was first proposed by Louis Agassiz, a Swiss-born biologist, who developed the foundational glacial theory that helps us understand these climate patterns.
Agassiz's work was revolutionary for his time. He observed evidence of glacial activity in areas that no longer had glaciers, leading him to propose that these regions had once been covered by ice. His theory initially faced significant resistance from the scientific community.
Effects of ice ages
Ice ages create extensive changes to Earth's systems beyond just erosion and deposition:
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Large-scale isostatic movement - The enormous weight of ice sheets causes the Earth's crust to sink, whilst their removal allows it to rebound upwards
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Disruption of river systems - Ice sheets block and redirect river flow patterns across continents
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Alteration of ocean and wind currents - Warm currents can no longer travel as far from the equator due to the presence of ice masses
These effects demonstrate how ice ages don't just affect the areas directly covered by ice. The entire global climate system becomes reorganised, affecting weather patterns, sea levels, and ecosystems worldwide.
How glaciers form
Glaciers develop as accumulated layers of ice and snow build up over hundreds and thousands of years. For glacier formation to occur, snow must accumulate faster than it melts.
Zone of accumulation: The area where snow and ice builds up, typically found along mountain ranges where temperatures remain consistently low.
The process begins in zones of accumulation, usually located in mountainous regions where temperatures stay below freezing. These glaciers gradually expand to fill entire valleys before moving downslope due to gravity. As they advance downslope, individual glaciers can join together to form ice sheets capable of covering entire continents - these are called continental glaciers.
The three stages of glacial ice formation
Glacial ice forms through a systematic three-stage process that can happen quickly or slowly depending on the rate of snow accumulation:
Worked Example: The Formation of Glacial Ice
Stage 1: Fresh snow accumulation Fresh snow falls and builds up on the ground. Newly fallen snow is very soft and easily compacted because it consists of 90% air.
Stage 2: Formation of firn As additional snow falls, the layers underneath become compressed. The pressure causes the snow to melt slightly before refreezing, transforming it into rounder, smaller grains of ice called firn. Firn contains 20-30% air.
Stage 3: Glacial ice formation
Continued snow accumulation compacts the firn grains further into solid, dense glacial ice. This glacial ice is also known as 'blue ice' because the compaction process has removed most oxygen from it, leaving only about 20% air as small bubbles.
Firn: Compacted snow that has been compressed into small, round ice grains containing 20-30% air.
Continental ice sheets
During the last ice age, continental ice sheets covered vast areas including Greenland, parts of North America, Northern Europe, and Antarctica. These massive ice formations developed when multiple glaciers joined together as they moved down from mountain ranges.
Continental glaciers represent the largest scale of ice accumulation, capable of covering entire continents and fundamentally reshaping global climate patterns and landscapes.
Currently, we are living in an interglacial period. Ice sheets from the last ice age still remain in Greenland, Antarctica, and mountainous regions such as the Alps, serving as reminders of this dramatic period in Earth's climate history.
The fact that we're currently in an interglacial period doesn't mean ice ages are over. Based on natural climate cycles, Earth would likely enter another glacial period in the future, though human activities and climate change may be altering these natural patterns.
Remember!
Key Points to Remember:
- The last ice age (Pleistocene period) lasted from 2.6 million to 10,000 years ago
- Ice ages involve at least five periods of glacial advance separated by warmer interglacial periods
- Glaciers form through a three-stage process: fresh snow → firn → glacial ice
- Ice ages cause major effects including isostatic movement and disruption of river and ocean systems
- We currently live in an interglacial period, with remaining ice sheets in Greenland, Antarctica, and mountain regions