What caused the landforms found in north america

Well there are many different kinds of landforms found in North America.

Landforms may be classified as depositional or erosional. Depositional landforms  have the character and shape of the deposits  of which they are made. They include  beaches, stream terraces, and alluvial fans  at the foot of mountains. Erosional landforms  are ones that have been created by agents  of erosion such as streams, rain, and ice.  The most widespread erosional landforms are  those made by running water acting over  very long periods of time.

There are more, but given the amount of info I have, I cannot give a more specific answer.

yes probably it reduce

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answerhydrogenous sediment;