These shifting plates cause volcanoes and earthquakes. Volcanoes are the most visible evidence of the turmoil and tumult that's taking place under the earth's crust all the time, with red hot lava and ash flying through the air. Like the lid on a pressure cooker, sometimes the lid blows off. When plates move away from each other, hot liquid rock, or magma, will seep up through the gaps. The collision causes openings in the earth's crust.
Pressure forces the magma up through the cracks, sometimes as far up as the earth's surface.
If magma finds a crack in the layer above it and moves into an area of lower pressure, gasses in the magma are released, just like the bubbles in a can of shaken carbonated soda. Wednesday Vulcanologists are scientists who study volcanoes. And they've invented a lot of complex scientific terms to describe what happens when a volcano actually erupts. That may have an obvious meaning to those of us who live in a dairy state. But to a vulcanologist, it means a chunk of thick lava that's propelled high into the air during a volcanic eruption.