Volcanoes are mountains that can spew fire, debris, smoke, lava. Scientists classify them according to their volcanic activity into active, dormant and extinct. There are several criteria by which a volcano can be classified as extinct.
Instructions
Step 1
Science has not come to an unambiguous definition of an extinct volcano. It is also difficult to divide volcanoes into extinct and dormant. Currently, a volcano is considered extinct if it has not been active for 10 thousand years.
Step 2
But even this definition is controversial, since firstly, the volcano can be activated after this period. This can be provoked, for example, by an earthquake. Secondly, there are few surviving historical descriptions of the eruptions.
Step 3
To establish the chronology of the eruptions, volcanologists conduct geological studies. You can find out how long ago the volcano erupted by the nature of the occurrence of volcanic rocks, determining their age using the radiocarbon method.
Step 4
The main features of a volcano are a crater, or caldera, and the layering of the rocks that form the cone. But over time, the extinct volcano collapses, erodes, the crater is eroded and covered with new layers of earth. Then it can be difficult to tell if the mountain is an extinct volcano.
Step 5
Scientists determine this by drilling wells and exploring the mines of extinct volcanoes. At the same time, the structure of rocks is studied, and the presence and composition of lavas and volcanic tuffs is analyzed.
Step 6
In addition, the extinct volcano retains signs of post-volcanic activity for a very long time, up to several million years. Manifestations of such activity are hot mineral springs and fumarole excretions. Fumaroles are volcanic gases emitted through cracks and have different temperatures - from 100 to 1000 degrees.
