They look like ordinary mountains off in the distance, beautiful against the pale blue sky, but what's inside that mountain is not ordinary, and sometimes, dangerous - even fatal. I'm talking about volcanoes. They're dotted all over the globe, north, south, east and west, some dormant and some not.
Volcanoes are mountains made up of various natural elements (including debris from previous explosions), but the huge rock is connected to reservoirs holding searing hot magma. And magma, being buoyant, rises, and as it rises more and more, the pressure decreases, resulting in expanding gasses. The expanding gasses send the magma flow through the Earth's crust and out into the open, through vents and fissures. We now have a volcanic eruption, and the magma that has erupted, is now called lava.
There are two different kinds of eruptions, however. The first is a lava flow, which means that the magma is runny and the gasses escape easily, and the lava flows down the side of the volcano. This kind of eruption doesn't kill often, for the people/animals can get away from the slow moving lava.
The second kind is an explosion, which is where the magma is thick and the expanding gasses are stuck inside. This results in the magma just exploding out of the volcano, sending tephra (airborne objects ejected from the volcano) raining down on the surrounding land. Lava flies through the sky with incredible power and speed, crashing into the ground and houses. Ash begins to rain down from the sky, blanketing the town in it. This eruption is very dangerous and deadly.
Volcanoes form when tectonic plates crash and collide together, or on the edge of a plate that has been lodged beneath another, which is how Mt. St. Helens was formed. And the ash, though it may resemble snow as it peacefully falls from the sky, can be catastrophic. Ash, when thrown from the volcano, often penetrates the atmosphere, which means an ash cloud can form together. Ash clouds are extremely dangerous, and can wrap around the entire planet.
Volcanoes are amazing and very interesting to learn about, but extremely harmful! It's probably best if we stick to the books.
"Volcano: a mountain with hiccups."
Author's Note: Sources: http://vulcan.wr.usgs.gov/Outreach/AboutVolcanoes/