Originally aired during the week of April 5, 1999
We tend to think of the ground we stand on as solid and permanent. And it is - sort of. But in the 1960's, earth scientists began to see our planets' surface as a series of thin, rigid slabs that float on earth's fluid insides. These plates are moving - very slowly to be sure - like carpets floating on warm, slow moving streams. We don't see or feel this happening - except when the plates pull apart or grind together. Then, look out! 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. The word "volcano" comes from the ancient Romans, who believed that volcanoes were caused by Vulcan, the god of fire who lived under Mt. Etna, a volcano in Sicily.
Every living thing on earth - you, me, plants, animals - live on thin continental plates - plates that are ever so slowly shifting on the red hot rock of the earth's mantle. Like the lid on a pressure cooker, sometimes the lid blows off. When that happens, we're looking at a volcano! When plates move away from each other, hot liquid rock, or magma, will seep up through the gaps. When two plates collide, one plate is often pushed or "subducted" beneath the other. 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. Remember what happens when you open a soft drink can that's been well shaken? 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.
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. Like: "cow-dung bomb." 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. Magma rises to the surface because it is less dense than the solid rock surrounding it. Great underground pressures can force lava, cinders and gases up to the earth's surface and high into the air. Some volcanoes spew runny lava that flows freely and rapidly down the cone - about 60 miles per hour! Others eruptions have a more oozy, molasses-like consistency. Lava erupts at temperatures over 2000 degrees Fahrenheit - super hot!
There are about 500 active volcanoes in the world (meaning they could erupt again at some time). When a really big volcano erupts, the energy released is hundreds to thousands of times greater than the atomic bombs dropped in WW II. Researchers are making progress in figuring out when a volcano may suddenly erupt, but it is not an exact science. Residents of the ancient city Pompeii found out how unpredictable volcanoes can be in 79 AD, when the nearby mountain suddenly erupted. The city was buried in a thick blanket of ash, killing 2,000 people. A 17 year-old named Pliny (PLIN e) the Younger survived the tragedy and wrote a vivid description of it. Today, really great eruptions are sometimes referred to as "Plinian." The 1980 eruption of Mt. St. Helens was Plinian. It devastated 230 sq. miles of forest.
The material that comes out of the "vent" or "fissure," of a volcano builds up a cone. This cone may develop into a very lofty mountain - volcanic peaks thousands of feet high were built layer by fiery layer! The cinder cone volcano is a kinder, gentler sort of volcano. Cinder cones are built from ejected lava fragments. They are small, as volcanoes go, seldom more than 1000 feet high. One such volcano formed in Mexico in 1942 in a corn field-a farmer and his wife watched it all happen. A few weeks prior to the eruption, the area experienced tremors; then one day smoke with a sulfur smell rose out of a hole that had been in the corn field for years. During that night, hot gasses hurled lava into the air. The next day, they saw a 150 foot cone. Five days later it was as high as 400 feet.
