By studying the tectonic plates, scientists found that the plates move, or float, because of the intense heat underneath them. There are immense pressures at work in the core, mantle and crust. Put together, these pressures cause the tectonic plates to move or slip, sometimes causing earthquakes, tsunamis, and volcanoes. The big continental plates include the Pacific Plate that extends almost to Japan and runs down the west side of North and South America. But it is the tiny Indian Plate that pushes northward into the largest plate of all: the Eurasian Plate. The collision of these two plates created the Himalaya and Karakoram mountain ranges. Earthquakes occur when two plates rub up against each other. Eventually, one plate will give way and slip under the other plate. This sudden movement, sometimes only one meter, has tremendous consequences. In the Pacific Ocean, tidal waves are started. The 2004 tsunami that swept across the Indian Ocean and hit Indonesia, Thailand, and Sri Lanka, killing 230,000 people, is an example of continental drift and plate tectonics.