How can the presence of wolves in Yellowstone National Park change the course of a river?

After the wolves came back less trouble was made and beavers began to build dams which began to help the rivers get back in shape.

Explanation:

Wolves were in to Yellowstone National Park in 1995. Wolves began hunting elk, which had destroyed willows and aspen along the park's waterways. The trees began to come back, and the beavers began to build dams with them. The rivers began to hold their course, and less erosion was evident.

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The wolves changed the behavior of the rivers. They began to meander less. There was less erosion. ... So the wolves, small in number, transformed not just the ecosystem of the Yellowstone National Park -This huge area of land... but also, its physical geography.

Explanation:

it cools slower in the earth meaning the crystals have more time to form than lava on the surface