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.
NoteIt's a common misconception that glaciers only respond to temperature changes. Precipitation also plays a critical role in their behavior.
HintHow to Map Glacial Retreat?
Why Study Glacial Retreat?
- Glaciers are often referred to as the "canaries in the coal mine" of climate change.
- Their retreat offers visible evidence of global warming and has significant implications, including rising sea levels, reduced freshwater availability, and ecosystem disruptions.
How Are Glacial Retreat Patterns Represented?
- Historical Maps and Satellite Imagery:
- Historical maps, often created through field surveys, provide a baseline for understanding past glacial extents.
- Modern satellite imagery offers precise, up-to-date data on glacier boundaries. By comparing these datasets, scientists can calculate the rate of retreat.
- Time-Series Maps:
- These maps illustrate the position of a glacier’s terminus (end point) at different time intervals. For example, a map might show the glacier’s extent in 1980, 2000, and 2020, with each year represented by a distinct color or line.
- Digital Elevation Models (DEMs):
- DEMs are 3D representations of terrain that help visualize changes in glacier thickness and volume over time, offering a more comprehensive picture of glacial retreat.
Natural Desertification
What is Desertification?
- Desertification is the expansion of desert-like conditions into previously fertile areas.
- It is driven by a combination of climate change and human activities.
Causes of Desertification
1. Climate Change
- Increasing Aridity: Higher temperatures and reduced rainfall intensify droughts.
- Shifting Weather Patterns: Changes in wind and precipitation can expand desert boundaries.
2. Human Activities
- Deforestation: Removing trees reduces soil stability and increases erosion.
- Overgrazing: Excessive livestock grazing depletes vegetation, exposing soil to degradation.
The Sahara Desert is expanding southward into the Sahel region, driven by prolonged droughts and unsustainable land use practices.
Impacts of Desertification
- Loss of Arable Land: Fertile soil becomes barren, reducing agricultural productivity and threatening food security.
- Changes in Ecosystems: Biodiversity declines as habitats are lost, and desert species replace those adapted to wetter conditions.
- Human Displacement: Desertification forces communities to migrate in search of arable land and water, leading to social and economic challenges.
Desertification is not limited to hot deserts. It can occur in semi-arid regions, such as parts of Central Asia, the American Southwest, and the Mediterranean (e.g. in Southern Spain).
HintHow to Identify Desertification Hotspots?
- Desertification is a complex process influenced by both natural and human factors. To identify hotspots - areas most at risk - scientists use a combination of maps and models.
How Are Desertification Hotspots Mapped?
- Vegetation Index Maps:
- Satellite data is used to create maps of vegetation health, often measured by the Normalized Difference Vegetation Index (NDVI). Declining NDVI values over time can indicate desertification.
- Soil Degradation Maps:
- These maps highlight areas where soil quality is deteriorating due to erosion, salinization, or nutrient depletion. They are often created by combining field surveys with remote sensing data.
- Overlay Maps:
- By overlaying datasets such as rainfall, land use, and population density, scientists can identify areas where multiple factors contribute to desertification. These are the hotspots most in need of intervention.
Comparing Glacial Retreat and Desertification
- While glacial retreat and desertification occur in vastly different environments, they share common drivers and consequences.
| Aspect | Glacial Retreat | Desertification |
|---|---|---|
| Primary Driver | Warming temperatures | Climate change and human activities |
| Key Impact | Formation of glacial lakes and altered rivers | Loss of arable land and biodiversity |
| Human Influence | Accelerated by fossil fuel use | Deforestation and overgrazing |
| Geographic Focus | Polar and high-altitude regions | Semi-arid and arid regions |
Why Do These Changes Matter?
- Ecosystem Services: Glaciers provide freshwater for billions, while fertile lands support agriculture.
- Global Impacts: Melting glaciers contribute to sea-level rise, and desertification exacerbates food insecurity.
- Human Resilience: Understanding these processes helps us develop strategies to adapt and mitigate their effects.
How do cultural perspectives influence our responses to environmental changes like glacial retreat and desertification? Consider the role of indigenous knowledge in these contexts.
