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 levels fall with ice sheet formation. b. River flow decreases as ice sheets expand. c. Rivers adjust by deepening or widening as glaciers melt.

Step-by-step solution

Understanding Ice Sheet Formation

When ice sheets form, a significant amount of water from the oceans is stored on land as ice. This process removes water from the ocean, causing a reduction in sea level. Essentially, as glaciers grow, the sea level falls.

Analyzing River Impact from Ice Sheet Expansion

As ice sheets expand, rivers flowing towards the ocean may experience reduced flow, as more water is locked up in ice. Additionally, the channels may change due to the land being pressed down by the ice sheets or due to the physical blockage of river paths by ice.

Predicting River Adjustments During Glacial Melting

When the ice sheets melt, the water returns to the ocean, raising sea levels. Rivers might carry increased flow due to meltwater from glaciers, possibly leading to rivers widening or deepening their channels. The increased flow can also result in further erosion and sediment transportation.

Key concepts

Effects of Glacial Expansion on Rivers

When glaciers or ice sheets expand, they significantly impact the rivers flowing towards the ocean. During these periods of expansion, a portion of a river's water can get locked up in the growing ice sheets. As a result, rivers tend to have reduced flow since less water is available to reach their destinations. This could be a challenge for river ecosystems reliant on a steady water supply.

Another result of ice sheet expansion is the physical alteration of the landscape. The massive weight of accumulating ice can press the ground downwards. This change in topography may redirect river channels, sending rivers on new paths. Additionally, the ice itself might serve as a physical barrier, directly blocking rivers and potentially altering their flow direction.

• Reduced river flow due to water storage in ice.
• Redirection or obstruction of rivers by ice.
• Potential ecosystem disruptions due to changes in river patterns.

River Adjustments During Glacial Melting

As ice sheets begin to melt, rivers undergo several adjustments. First, meltwater from glaciers contributes to an increased flow in rivers. This rise in water volume can cause rivers to widen or deepen their channels. The excess water has the potential to reshape the landscape by eroding riverbanks and carrying sediment downstream.

The increased flow from glacial melt can lead to both positive and negative outcomes. On one hand, the spread of nutrient-rich sediment can enrich agricultural lands. On the other hand, it could lead to increased flooding risks in areas not capable of managing the sudden rise in water.

• Increased river flow due to melting glaciers.
• Potential for river channels to widen or deepen.
• Enhanced erosion and sediment transport.
• Flooding risks and nutrient distribution changes.

Glaciation Impact on Sea Level

Ice sheets and glaciation have a profound impact on global sea levels. When ice sheets form and expand, they essentially lock away vast amounts of water, resulting in a lower sea level. This occurs because the water that contributes to the growth of these ice sheets is drawn out of the oceans.

Conversely, as these ice sheets melt, the water is released back into the ocean, raising sea levels. This process of sea level fluctuation has played a significant role over the geological timescale, profoundly impacting coastal environments. Rising sea levels can lead to the submersion of low-lying areas, altering habitats and affecting human settlements.

• Sea level falls as water is stored in expanding ice sheets.
• Increased sea levels as ice sheets melt.
• Impact on coastal environments and potential for habitat change.