Listen to part of a lecture from a geology class.
(female professor) So, when we look at lakes, they seem to be permanent, we assume they'll be around forever. But in fact, lakes aren't permanent; they can actually disappear. Sometimes they disappear through natural processes, and sometimes because of human activities.First let's look at one way that lakes can disappear naturally, and that is, by gradually getting filled in with organic sediment. This often happens with lakes that have lots of plants growing in them. When the plants die, they break down into a muddy substance, which falls to the bottom of the lake, they're then replaced by new plants, which eventually also die and fall to the bottom. And over the years, all this dead plant material builds up on the bottom of the lake, and as builds up, it starts to fill up the lake, and there's less and less room for water, and eventually the lake gets completely filled in, and disappears.OK, lakes can also disappear,pretty rapidly sometimes, as a result of human activities. For example, we know that farmers need water to irrigate their crops. And sometimes to get that water, they pump that water out of a nearby lake. They install pipes that run from the lake to their farms, and they pump the water out of the lake and into their fields. Now that’s ok if the lake is continually being refilled with rainwater or with water from streams that run into the lake, but if there isn’t enough rainwater or stream water to replace the water the farmers take out of the lake, the lake will eventually dry up.
Using points and examples from the lecture, describe two ways that lakes can disappear.
One way that rivers or lakes disappear is by natural process. That is, the lake or river is gradually filled up with organic sediments. It usually happens with the lake or river where there're plenty of plants growing in it. When the plants die, they break into muddy substances that fall to the bottom of the lake or river, and then new plants grow on it, die on it, and again, become sediments over the first layer of debris. Over time, those sediments will pile up on the bottom of the lake or river until one day it gets completely filled in. Another is by human activities. Farmers need water to irrigate their crops, so sometimes they build pipes in nearby rivers or lakes to get water from them. Normally, the river or lake can be refilled by rainwater or streams that run into it. But in case of lack of refill, like drought, the lake or river will soon dry up. (156 words)
