The appalachian mountains may have once been as lofty as the himalayan-tibetan mountain belt is today. why are they not this high now? the appalachian mountains may have once been as lofty as the himalayan-tibetan mountain belt is today. why are they not this high now? opening of the north atlantic ocean converted lithosphere to asthenosphere beneath eastern north america, forcing eastern north america to sink to low elevations. they developed a dense crustal root following collision, and isostasy forced them to sink to their present elevation. they formed long ago, and erosion has beveled them to their present low elevation. the mountains cooled following the collision, which increased the density of the of the rocks by cooling, and isostasy forced the mountains to sink.

The correct answer is - They formed long ago, and erosion has beveled them to their present elevation.

The Appalachian Mountain Range is one of the oldest mountain ranges on the planet. They have formed in the Ordovician Period, around 480 million years ago. When they formed and were at their peak, the Appalachians were much larger and higher than what they are in the present. The reason for their decline in size is attributed to the erosion. The erosion is a process that removes the material from its original position. This process has been influencing, at different rates, the Appalachians for almost half a billion years. Even though the erosion is not a process that acts very quickly, when put the time that it influenced these mountains we will see that it managed to lower them significantly. That process continues in the present, and in the manner in which the continents are moving, there shouldn't be any force that will help lift up the Appalachians again, but instead they will continue to shrink until they are flattened in the distant future.

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