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Listen to a lecture in a geology class, take detailed notes while listening.
expand – to get larger and/or wider
precondition – something, necessary for something else to happen
tropics – hot humid areas near the equator
volume – an amount of something
wedge – something used to force something else apart
Fill in the following diagram.
Step 1.
Step 2.
Step 3.
Step 4.
Now answer the questions using your notes.
Ice Weathering
Summarize the text using your notes and diagram.
- Step 1: Water gets into the crack of a rock.
- Step 2: Water freezes and expands.
- Step 3: Ice acts as a wedge to expand the crack.
- Step 4: Ice thaws leaving a bigger crack.
Listen again:
M: Now, let's talk about the role of ice in weathering. Like water and wind, ice is responsible for weathering rocks, or, urn, breaking them down. However, for ice weathering to occur, you need two particular preconditions. You need to have water, and you need to have temperatures cold enough to turn that water into ice. So don't expect to find lots of ice weathering in the tropics.
Okay, so here's how it works. While the temperature is above freezing, water flows into cracks in rocks. Then, as the temperature drops, the water freezes, and, most importantly, it expands. In fact, its volume increases by nine percent. The ice then acts like a wedge, placing enormous pressure on the crack and expanding it, Finally, the ice melts, leaving a now wider crack in the rock. This process often happens many time's before the rock is weakened enough to break. It may be hard to believe, but something as simple as water freezing can break down entire mountains. Next time you see a pile of broken rocks at the base of a cliff, think about ice weathering.
