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Glaciers & Ice Ages Cheat Sheet
A printable reference covering glacier formation, glacial movement, erosion, deposition, ice age causes, and climate evidence for grades 6-10.
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Glaciers are large masses of ice that form on land and move slowly under their own weight. This cheat sheet helps students connect glacier formation, movement, erosion, and deposition to the landforms seen on Earth today. It also explains how ice ages happen and how scientists study past climates. These ideas are important for understanding landscapes, sea level, and long-term climate change. The core idea is that glaciers form where more snow accumulates in winter than melts in summer over many years. Gravity causes glacial ice to flow downhill or outward, carrying rock material that can scrape, carve, and reshape land. Glaciers erode by plucking and abrasion, then deposit sediment as till, moraines, and outwash. Ice ages are linked to changes in Earth's orbit, atmospheric gases, ocean circulation, and feedbacks such as ice-albedo feedback.
Key Facts
- A glacier forms when annual snow accumulation is greater than annual melting for many years, so snow compacts into firn and then glacial ice.
- The glacier mass balance is accumulation minus ablation, where positive mass balance means the glacier gains ice and negative mass balance means it loses ice.
- Glaciers move by internal flow of ice and by basal sliding when meltwater reduces friction at the glacier bed.
- Glacial erosion happens mainly by plucking, which pulls rocks from the ground, and abrasion, which scrapes bedrock like sandpaper.
- A U-shaped valley forms when a glacier widens and deepens a river valley that was originally V-shaped.
- Glacial deposits include till, which is unsorted sediment, and outwash, which is sorted sediment carried by meltwater streams.
- Moraines are ridges of till, and a terminal moraine marks the farthest advance of a glacier.
- Ice ages are long cold periods when continental ice sheets expand, often influenced by Milankovitch cycles, greenhouse gas levels, ocean circulation, and ice-albedo feedback.
Vocabulary
- Glacier
- A large, long-lasting mass of ice on land that moves under its own weight.
- Accumulation
- The gain of snow and ice on a glacier, mainly from snowfall.
- Ablation
- The loss of ice from a glacier by melting, sublimation, calving, or wind erosion.
- Moraine
- A ridge or pile of unsorted sediment deposited directly by a glacier.
- Ice Age
- A long interval of Earth's history when global temperatures are cooler and ice sheets cover large areas of land.
- Ice-Albedo Feedback
- A climate feedback in which bright ice reflects sunlight, cooling Earth and allowing more ice to form.
Common Mistakes to Avoid
- Confusing glaciers with sea ice is wrong because glaciers form on land, while sea ice forms when ocean water freezes.
- Thinking glaciers do not move is wrong because glacial ice flows slowly downhill or outward due to gravity and pressure.
- Assuming all glacier sediment is sorted is wrong because till is unsorted, while meltwater outwash is usually sorted by particle size.
- Mixing up U-shaped and V-shaped valleys is wrong because rivers usually cut V-shaped valleys, while glaciers carve wider U-shaped valleys.
- Saying ice ages are caused by one factor only is wrong because orbital changes, greenhouse gases, ocean circulation, and feedbacks work together.
Practice Questions
- 1 A glacier gains 80 cm of snow and ice in a year and loses 55 cm by melting and calving. What is its mass balance, and is it gaining or losing ice?
- 2 A glacier advances 18 meters in 6 days. What is its average rate of movement in meters per day?
- 3 A field sample contains mixed clay, sand, gravel, and boulders with no clear layers. Is it more likely till or outwash, and why?
- 4 Explain how ice-albedo feedback can make a cooling climate become even colder during the start of an ice age.