The eruption of Cerro Negro Volcano, near Leon, Nicaragua, during November 1968.
U. S. Department of the Interior / U. S. Geological Survey
Volcanoes
by Robert I. Tilling
Cover and Title Page: Lava fountains and flows, Mauna Loa, Hawaii, July 6, 1975.
Volcanoes destroy and volcanoes create. The catastrophic eruptionof Mount St. Helens on May 18, 1980, made clear the awesomedestructive power of a volcano. Yet, over a time span longer thanhuman memory and record, volcanoes have played a key role in formingand modifying the planet upon which we live. More than 80 percentof the Earth’s surface—above and below sea level—is of volcanicorigin. Gaseous emissions from volcanic vents over hundreds ofmillions of years formed the Earth’s earliest oceans and atmosphere,which supplied the ingredients vital to evolve and sustain life. Overgeologic eons, countless volcanic eruptions have produced mountains,plateaus, and plains, which subsequent erosion and weatheringhave sculpted into majestic landscapes and formed fertile soils.
Ironically, these volcanic soils and inviting terranes have attracted,and continue to attract, people to live on the flanks of volcanoes.Thus, as population density increases in regions of active or potentiallyactive volcanoes, mankind must become increasingly aware of thehazards and learn not to “crowd” the volcanoes. People living in theshadow of volcanoes must live in harmony with them and expect, andshould plan for, periodic violent unleashings of their pent-up energy.
This booklet presents a generalized summary of the nature, workings,products, and hazards of the common types of volcanoes aroundthe world, along with a brief introduction to the techniques of volcanomonitoring and research.
On August 24, A.D. 79, VesuviusVolcano suddenly exploded anddestroyed the Roman cities ofPompeii and Herculaneum. AlthoughVesuvius had shown stirringsof life when a succession ofearthquakes in A.D. 63 causedsome damage, it had been literallyquiet for hundreds of years and wasconsidered “extinct.” Its surfaceand crater were green and coveredwith vegetation, so the eruption wastotally unexpected. Yet in a fewhours, hot volcanic ash and dustburied the two cities so thoroughlythat their ruins were not uncoveredfor nearly 1,700 years, when thediscovery of an outer wall in 1748started a period of modern archeology.Vesuvius has continued itsactivity intermittently ever since A.D.79 with numerous minor eruptionsand several major eruptions occurringin 1631, 1794, 1872, 1906 andin 1944 in the midst of the Italiancampaign of World War II.