Hills are easier to climb than mountains. They are less steep and not as high. But, like a mountain, a hill will usually have an obvious summit, which is its highest point. According to the U.S. Geological Survey, there is no official difference between hills and mountains.
Geothermal heat- to provide energy for process like subduction, melting and metamorphism (to drive plate tectonics)
solar energy- for processes like erosion, weathering and transport
That depends on how close you are to the equator, in coulombia the temperature barely changes wile in south Canada it changes every season