The Appalachian Mountains were once higher than they are now. Which of these explains why the Appalachians have become shorter over the years?
A.
plate movements
B.
volcanic eruptions
C.
deposition of sediments
D.
erosion by water and wind
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D. erosion by water and wind
The correct answer is D. erosion by water and wind. Over the years, the Appalachian Mountains have undergone significant erosion, primarily due to the action of water and wind. Here's how you can arrive at this answer:
First, let's eliminate some options. B, volcanic eruptions, can be ruled out because the Appalachian Mountains were not formed by volcanic activity. Volcanic eruptions would be more relevant to explaining changes in mountain ranges formed by volcanic activity, like the Cascade Range in the western United States.
Next, we need to consider whether plate movements or deposition of sediments could be the reason behind the Appalachian Mountains becoming shorter. While plate movements do shape the Earth's surface and are responsible for the formation of mountain ranges, they are not the main factor in the current height reduction of the Appalachians.
This leaves us with C, deposition of sediments, and D, erosion by water and wind. Deposition of sediments is when sediment particles settle out of a fluid and accumulate over time. While this process can add material and potentially increase the height of certain landforms, it is not the primary reason why the Appalachian Mountains have become shorter.
On the other hand, erosion refers to the wearing away of land by natural processes such as water and wind. Over millions of years, the Appalachians have been subjected to the constant forces of weathering, water flow, and wind. These processes gradually break down the rocks that make up the mountains, resulting in the loss of height. This makes D, erosion by water and wind, the most accurate explanation for why the Appalachian Mountains have become shorter over time.