Volcanic Mountains are the results of Volcanic eruptions, as the magma (that is produced with in the upper parts of earths mantle) shoots out of a vent and cools it builds on itself and forms hills or mountains.  Magma that breaks the earth's surface and erupts from a volcano is called Lava which is one of the hottest liquid substances around. As the lava cools it forms volcanic rocks.  Sometimes ash also comes out of a volcano and can pollute the air for miles. Volcanoes aren't just an earth based phenomenon either, there is evidence that volcanoes have or do exist/ed on Mars and Venus, and even our own Moon. 
 
Tsunamis and Tidal Waves are two diffrent things. Tsunamis are waves that are caused by either landslides, volcanoes or earthquakes (common).  This movement of the sea floor either up or down will raise or lower the water above it creating a wave, the size of a Tsunami wave depends on the area that moves on the ocean bottom and how far it moves.  Tidal waves on the other hand are waves that are caused by the pull of the moon. a natural tidal bore (as they are sometimes called) is an example of a self-reinforcing solitary wave.
 
Floods occure for many reasons most having to do with rains and storms. Flash floods are any sudden and severe flood event. Floods sometimes occure when the terrain of a certian area won't  absorb water (due to lack of vegitation, soil type,ect).  Sometimes ice jams cause floods, as ice sheets on water at times form dams when they are pressed against something (a bolder, or a group of trees).