Question

Several times during the past 2.5 million years, huge ice sheets (continental- size glaciers) formed and spread across large parts of Northern Hemisphere landmasses and then gradually melted away. a. How do you think the formation of ice sheets affected sea level? b. How would rivers flowing into the ocean have been affected as the ice sheets expanded? c. What kind of adjustments would these rivers make as the glacial ice melted?

Short answer

a) Sea level fell with ice sheet formation. b) Rivers had reduced flow. c) Rivers increased flow as ice melted.

Step-by-step solution

Effect of Ice Sheets on Sea Level

When ice sheets form, they capture large volumes of water that would otherwise be in the ocean. This water is locked in a solid state as ice on land, reducing the overall volume of liquid water in the ocean. As a result, the sea level falls when ice sheets form.

Impact on River Flow into Oceans

As ice sheets expand, more water is trapped as ice, decreasing the amount of water available to flow in rivers. Reduced river discharge into the oceans can be expected, leading to lower river levels and possibly slower flow rates.

River Adjustments as Ice Melts

When glacial ice melts, it returns a large volume of water back to the ocean and rivers. Rivers may experience increased flow rates and higher water levels. They may also adjust their courses and sediment transport patterns as they cope with the increased volume and speed of water.

Key concepts

Continental Glaciers

Continental glaciers are massive ice sheets that cover significant portions of continents. These glaciers have played a crucial role in shaping the Earth's landscape during periods known as ice ages.
Formed over thousands of years, these glaciers can spread across large parts of land masses, particularly in the Northern Hemisphere. As they grow, continental glaciers trap vast amounts of water, leading to changes in sea levels.
When these glaciers form, the water that would otherwise reside in oceans is locked in a solid state, causing global sea levels to drop. This phenomenon, known as eustatic sea level change, highlights the dynamic relationship between ice sheets and our planet's oceans.

Impact on River Systems

The expansion of continental glaciers significantly impacts river systems. As glaciers grow, they sequester water that would naturally flow into rivers. This reduced water availability causes lower river levels.
A decreased water flow affects how rivers behave. With less water to carry, rivers may slow down, impacting the ecosystem and organisms dependent on steady flow rates. Rivers might become narrower and shallower, altering their sedimentation patterns.

• Reduces river discharge
• Lowers water levels
• Can slow down river flow

Overall, the changes in river systems can have widespread ecological impacts, affecting both aquatic life and human activities reliant on these waterways.

Glacial Meltwater Effects

As continental glaciers melt, they release enormous amounts of water back into the environment. This process has significant effects on both river systems and sea levels.
Rivers begin to receive increased water flows, leading to higher water levels and faster flow rates. Such changes can lead rivers to alter their courses, expanding their banks and changing sediment transportation.
Increased water discharge can:

• Cause flooding in certain areas
• Increase sediment transport
• Alter the river courses

These transformations require rivers to adjust, impacting nearby lands and ecosystems. Furthermore, the influx of meltwater contributes to rising sea levels, triggering changes in coastal regions globally.