Temporal Shifts in Landscapes
- Landscapes are not static, they evolve over time due to natural processes and human influences.
- Two significant phenomena that illustrate these changes are glacial advance and retreat and natural desertification.
Glacial Advance and Retreat
How Glaciers Work: A Balance of Forces
- Glaciers are dynamic systems governed by a balance between accumulation (snowfall and ice gain) and ablation (melting, evaporation, and ice loss).
- This balance determines whether a glacier advances or retreats.
When Glaciers Advance
- Accumulation grater than Ablation: More snow and ice are added than lost.
- Result: The glacier thickens and moves forward, reshaping the landscape through erosion.
When Glaciers Retreat
- Ablation grater than Accumulation: More ice melts than is replaced.
- Result: The glacier thins and recedes, leaving behind distinctive features like moraines and glacial lakes.
Remember: Glaciers don't "move backward" during retreat. Instead, they melt faster than they advance, causing the ice front to shrink.
The Impact of Glacial Advance and Retreat
1. Formation of Glacial Lakes
- As glaciers retreat, they often leave behind depressions that fill with meltwater, forming glacial lakes.
- These lakes can be temporary or long-lasting, depending on the stability of the surrounding landscape.
The Great Lakes in North America were formed by retreating glaciers at the end of the last Ice Age.
2. Changes in River Systems
- Glacial meltwater can alter river courses, creating braided rivers or new drainage patterns.
- During glacial advance, rivers may be blocked or redirected by ice.
In Iceland, glacial rivers like the Jökulsá á Fjöllum have carved dramatic canyons as they adjusted to changing ice cover.
Why Do Glaciers Advance and Retreat?
- Climate Change: Warmer temperatures increase melting, while cooler periods enhance accumulation.
- Human Activities: Deforestation and urbanization can alter local climates, affecting glacial dynamics.
- Natural Cycles: Long-term climate patterns, such as ice ages, drive significant glacial changes.
Rapid Glacial Retreat in Iceland
Since 2000, the area of Iceland’s glaciers has decreased by ca. 800 km2, and by almost 2200 km2 since the end of the 19th century when the glaciers reached their maximum extent since the country’s settlement in the 9th century.
It's a common misconception that glaciers only respond to temperature changes. Precipitation also plays a critical role in their behavior.
