What kind of landform has a vent at the top, spews lava, steam, and pieces of rock?

What kind of landform has very steep sides that were cut by a river's erosion and time?

You get to this landform when oceans run dry. They're broad, flat spaces under the sky.

What kind of landform is tallest of all, with a spiky top where snow may fall?

What kind of landform is a huge chunk of water that takes up three-fourths of the Earth, and is salty?