USA Permafrost Landforms Quiz
Explore ice wedges, thaw lakes, and permafrost regions of Alaska (10 questions).
USA Permafrost Landforms Quiz: Quick Study Notes
Permafrost, ground that remains frozen for at least two consecutive years, is a defining feature of vast landscapes, primarily found in Alaska within the United States. This frozen ground gives rise to unique landforms like intricate ice wedge polygons and expansive thaw lakes, profoundly shaping the Arctic and sub-Arctic environments. Understanding these permafrost landforms is crucial for comprehending the dynamics of cold regions and their response to climate change.
Ground remaining frozen ≥2 years, extensive in Alaska. Contains vast organic carbon stores.
Formed by thermal contraction cracks filling with water & freezing repeatedly, creating distinct surface patterns.
Depressions formed by thawing ice-rich permafrost, leading to ground subsidence and water accumulation.
Approximately 80% of Alaska is underlain by permafrost, with continuous zones in the Arctic Coastal Plain.
Key Takeaways on USA Permafrost Landforms:
- Permafrost is subsurface ground that stays frozen for two or more years, common across about 80% of Alaska.
- Ice wedges develop from seasonal cracking of permafrost, filling with water and freezing to form distinctive polygonal patterns on the surface.
- Thaw lakes, or thermokarst lakes, are depressions created when ice-rich permafrost melts, causing the ground to subside.
- The active layer is the uppermost ground that thaws each summer and refreezes in winter, lying above the permafrost.
- Alaska hosts various permafrost types, from continuous in the north to discontinuous and sporadic further south.
- Thawing permafrost contributes to greenhouse gas emissions due to decomposing organic matter, impacting global climate.
- Permafrost landforms are vital indicators of Arctic environmental change and ecosystem health.
Frequently Asked Questions about USA Permafrost:
What is permafrost, and where is it found in the USA?
Permafrost is ground (soil, rock, or sediment) that remains frozen for at least two consecutive years. In the USA, it is predominantly found in Alaska, underlying about 80% of the state.
How do ice wedges form, and what do they look like on the surface?
Ice wedges form when very cold temperatures cause the ground to contract and crack. Water then fills these cracks, freezes, and expands. Over many years, repeated freezing and thawing cycles cause the ice to grow, forming large, wedge-shaped ice masses. On the surface, they often create distinctive polygonal patterns.
What are thaw lakes, and why are they important?
Thaw lakes, also known as thermokarst lakes, are depressions filled with water that form when ice-rich permafrost melts and the overlying ground subsides. They are important because their formation and expansion can release significant amounts of methane and carbon dioxide from previously frozen organic matter into the atmosphere, contributing to climate change.
Which regions of Alaska have significant permafrost?
Almost all of Alaska is underlain by permafrost to some extent. The northern regions, such as the Arctic Coastal Plain and the Brooks Range, have continuous permafrost, meaning it underlies 90-100% of the land. Further south, permafrost becomes discontinuous or sporadic.
What is the “active layer” in a permafrost environment?
The active layer is the topmost layer of ground in a permafrost region that thaws during the warmer summer months and refreezes completely during the winter. Its depth can vary significantly depending on factors like climate, vegetation, and soil type, and it is where most biological activity occurs.
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