Are all volcanoes alike?

We know of about 500 active volcanoes, and thousands more are rated as dormant or extinct. Lava rocks, crater lakes and other signs on the face of the earth tell of countless volcanoes that lived and died before the dawn of history. Volcanoes, active and extinct, also exist in great numbers on the floors of the oceans.

Of all the countless volcanoes, past and present, no two are exactly alike. Each builds its particular shape from its own rocky materials. Each follows its own history of dramatic events. Although there are no exact duplicates, there are certain similarities in volcanic activity. We can classify several types of volcano and their activities.

Stromboli, on an island north of Sicily is a volcano of the explosive type. Every ten minutes or so, a lump of fiery red lava is hurled above the crater. This explosive volcano shines for miles as a beacon known to sailors as the Lighthouse of Mediterranean.

Vesuvius, near Naples, tends to erupt in fiery fury after a long period of quiet. It is believed that the eruption is fed by a pool of lava some three miles below a surface layer of limestone. Carbon dioxide from the limestone dissolves in the molten lava, and pours into the air during an eruption.

Mount Pelee of the West Indies is the same type as Vesuvius. Its rare eruptions, however, carry fiery clouds of superheated steam and seething fragments of dust. Mount Katmai of Alaska also erupts with a fiery cloud, pouring down its slopes at 300 miles an hour.

Mauna Loa of Hawaii is a shield type volcano. Its masses of lava ooze up from below the ocean, forming a wide plateau with gentle slopes. Other lava plateaus are built from lava oozing from fissures, or long cracks in the earth’s crust. In 1783, in Iceland, flows of lava issued from such a fissure 20 miles long. In the remote past, lava oozed from such fissures in our Pacific northwest. These ancient, fire formed rocks cover 200,000 square miles.

The history of each volcano is decided by the earths crust, The pool of magma is a mixture of molten rocks steam and various gases, maybe 30 miles below the surface. The vent through which it erupts may be small or wide, or there may by a network of vents. The rocks which line the vents, such as the limestones of Vesuvius, also add individual character to each volcano.

In 143, a new volcano erupted from a small hole in a Mexican cornfield. In two years it formed a steep sided mountain 1,500 feet high. It now seems to be extinct. The progress of this volcano, Paracutin, was studied scientifically and it yielded much new information. Our knowledge of the rocks below the earthts crust and the forces that operate there is still, however, mainly guesswork, and volcanoes, even to the expert, are shrouded in mystery.