Earth Science: Glaciers, Ice Sheets, and Sea Level Worksheet

Question 1

Explain the difference between a glacier, an ice sheet, and sea ice. Include which of these can directly raise global sea level when it melts.

Accepted Answer

A glacier is a moving mass of land ice, usually in a mountain valley or polar region. An ice sheet is a very large mass of land ice covering more than 50,000 square kilometers, such as the Greenland or Antarctic Ice Sheet. Sea ice is frozen ocean water, and melting sea ice does not directly raise global sea level because it is already floating. Melting glaciers and ice sheets can directly raise global sea level because they add water from land to the ocean.

Question 2

A glacier has an accumulation zone where snowfall adds ice and an ablation zone where melting and sublimation remove ice. If annual accumulation is 1.4 meters water equivalent and annual ablation is 1.9 meters water equivalent, what is the glacier's annual mass balance? State whether the glacier is gaining or losing mass.

Accepted Answer

The annual mass balance is 1.4 meters minus 1.9 meters, which equals -0.5 meters water equivalent. The negative value means the glacier is losing mass for the year.

Question 3

Describe two ways glaciers move. Your answer should include internal deformation and basal sliding.

Accepted Answer

Glaciers move by internal deformation when ice crystals slowly bend and flow under pressure. They can also move by basal sliding when meltwater at the base reduces friction and allows the glacier to slide over bedrock or sediment.

Question 4

A tide gauge records that relative sea level at a coastal city is rising 6.0 millimeters per year. Satellite data show global mean sea level is rising 3.5 millimeters per year. What is the likely rate of local land subsidence or uplift at the city, and which one is it?

Accepted Answer

The local vertical land motion is 6.0 millimeters per year minus 3.5 millimeters per year, which equals 2.5 millimeters per year of subsidence. The city is sinking relative to the ocean, causing relative sea level to rise faster than the global average.

Question 5

A graph shows global mean sea level rising slowly from 1900 to 1990 and rising more steeply from 1990 to the present. What does the steeper slope after 1990 indicate about the rate of sea level rise?

Accepted Answer

The steeper slope indicates that the rate of sea level rise increased after 1990. A steeper line on a sea level graph means sea level is gaining height more quickly per year.

Question 6

List three major contributors to modern global sea level rise and briefly explain how each one adds to sea level.

Accepted Answer

Thermal expansion contributes because warmer seawater takes up more volume. Melting mountain glaciers contribute by adding land-based meltwater to the ocean. Melting ice sheets in Greenland and Antarctica contribute by transferring large amounts of land ice into the ocean as meltwater or icebergs.

Question 7

If 500 cubic kilometers of land ice melt and enter the ocean in one year, estimate the global mean sea level rise in millimeters. Use an ocean surface area of 361 million square kilometers and assume 1 cubic kilometer spread over 1 million square kilometers raises sea level by 1 millimeter.

Accepted Answer

The sea level rise is 500 cubic kilometers divided by 361 million square kilometers, using the shortcut that 1 cubic kilometer over 1 million square kilometers equals 1 millimeter. This gives 500 divided by 361, or about 1.39 millimeters. The estimated global mean sea level rise is about 1.4 millimeters.

Question 8

Explain why melting of the Greenland Ice Sheet is especially important for future sea level, even though it does not cover the largest area of ice on Earth.

Accepted Answer

The Greenland Ice Sheet is important because it contains enough land ice to raise global sea level by several meters if it melted extensively. It is also located in a region where warming can increase surface melting, reduce reflectivity, and speed up ice loss through outlet glaciers.

Question 9

What is albedo, and how can a decrease in albedo accelerate glacier or ice sheet melting?

Accepted Answer

Albedo is the fraction of sunlight that a surface reflects. Clean snow and ice have high albedo, so they reflect much sunlight. When albedo decreases because of melting, dust, soot, or exposed darker ice, the surface absorbs more solar energy and melting can accelerate.

Question 10

A glacier's terminus retreated 1.8 kilometers between 2005 and 2020. Calculate the average retreat rate in meters per year.

Accepted Answer

The time interval is 15 years. A retreat of 1.8 kilometers equals 1,800 meters. The average retreat rate is 1,800 meters divided by 15 years, which equals 120 meters per year.

Question 11

Study a diagram of an ice shelf attached to an ice sheet. Explain why collapse of a floating ice shelf does not directly raise sea level much, but can still lead to faster sea level rise later.

Accepted Answer

A floating ice shelf has already displaced ocean water, so its collapse does not directly raise sea level much. However, an ice shelf can act as a buttress that slows land-based ice flowing into the ocean. If the shelf collapses, glaciers behind it may speed up and deliver more land ice to the ocean, causing sea level to rise later.

Question 12

A coastal community is planning for future hazards. Identify two sea level rise impacts and one adaptation strategy for each impact.

Accepted Answer

One impact is more frequent coastal flooding, and an adaptation strategy is to elevate buildings or improve flood barriers. Another impact is saltwater intrusion into groundwater, and an adaptation strategy is to protect freshwater wells, reduce pumping near the coast, or develop alternative water supplies.

Earth Science: Glaciers, Ice Sheets, and Sea Level

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