TPO49-L1 Permafrost and thaw lakes in Alaska
Listen to part of a lecture in a geology class.
- What is the main purpose of the lecture?
[CHOOSE 2 ANSWERS]
- A. To contrast how different kinds of thaw lakes grow
- B. To explain why a new theory of thaw lakes is gaining acceptance
- C. To explain how processes in permafrost lead to the formation of thaw lakes
- D. To describe two competing theories about the growth of thaw lakes
- The professor explains thaw lake formation as a cycle of events that occur repeatedly.
[Summarize this cycle, and put them in order.]
- A.Meltwater flows into cracks in permafrost
- B.Ice wedges inside permafrost completely melt
- C.Freezing water expands cracks in permafrost
- D.Ice in the active layer melts as temperatures rise
- E.Permafrost shrinks and cracks as temperatures drop
- What is the significance of the “protective shelf” discussed by the professor?
- A. It prevents the slumping of lake banks.
- B. It shields the lake surface from strong winds.
- C. It redirects the waves to lake banks that do not face the wind.
- D. It allows the lakes to grow in the same direction as the wind blows.
- According to the thaw slumping model, which side of a thaw lake grows fastest?
- A. The side where the bank is shortest
- B. The side least exposed to wind
- C. The side that is at the highest elevation
- D. The side opposite the protective shelf
- What is the professor’s opinion of the thaw slumping model?
- A. He thinks it was urgently needed.
- B. He is not convinced that it has a firm basis.
- C. He thinks it would be better if it were simplified.
- D. He does not think it is very different from the old model.
- Why does the professor say this: 🎧
- A. He wants some information from the students.
- B. He thinks that the students may find an example helpful.
- C. He realizes that he forgot to mention an important topic.
- D. He wants to point out an important difference between frozen ground and dry ground.
CD EDACB C A B B