Hi there!
This can be called a hill.
An Isosceles triangle has two even parts, you add them up. For example 60 degree plus another 60 degree angle is 120 degrees. And the limit is 180 degrees, so in order to get that last angle, you'd have to subtract 160 from 180. And that'd be 20 degrees. I couldn't see the question but I hope this helps you in a way
Volcanic eruptions and/or earthquakes caused by the shifting of tectonic plates
One type of weathering is man made weathering. (For example) Humans may carve a rock or mine for minerals. Another type is natural weathering. This is when a river may push a rock or lighting may scratch a tree. That weathering is naturally occurring. Hope that helped!