by Robert I. Tilling
[Illustration: Cover and Title Page: Lava fountains and flows, Mauna
Loa, Hawaii, July 6, 1975.]
Volcanoes destroy and volcanoes create. The catastrophic eruption of
Mount St. Helens on May 18, 1980, made clear the awesome destructive
power of a volcano. Yet, over a time span longer than human memory and
record, volcanoes have played a key role in forming and modifying the
planet upon which we live. More than 80 percent of the Earth’s
surface—above and below sea level—is of volcanic origin. Gaseous
emissions from volcanic vents over hundreds of millions of years formed
the Earth’s earliest oceans and atmosphere, which supplied the
ingredients vital to evolve and sustain life. Over geologic eons,
countless volcanic eruptions have produced mountains, plateaus, and
plains, which subsequent erosion and weathering have 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
potentially active volcanoes, mankind must become increasingly aware of
the hazards and learn not to “crowd” the volcanoes. People living in the
shadow of volcanoes must live in harmony with them and expect, and
should 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 around the world,
along with a brief introduction to the techniques of volcano monitoring
and research.
[Illustration: ]
On August 24, A.D. 79, Vesuvius Volcano suddenly exploded and destroyed
the Roman cities of Pompeii and Herculaneum. Although Vesuvius had shown
stirrings of life when a succession of earthquakes in A.D. 63 caused
some damage, it had been literally quiet for hundreds of years and was
considered “extinct.” Its surface and crater were green and covered with
vegetation, so the eruption was totally unexpected. Yet in a few hours,
hot volcanic ash and dust buried the two cities so thoroughly that their
ruins were not uncovered for nearly 1,700 years, when the discovery of
an outer wall in 1748 started a period of modern archeology. Vesuvius
has continued its activity intermittently ever since A.D. 79 with
numerous minor eruptions and several major eruptions occurring in 1631,
1794, 1872, 1906 and in 1944 in the midst of the Italian campaign of
World War II.
[Illustration: ]
In the United States on March 27, 1980, Mount St. Helens Volcano in the
Cascade Range, southwestern Washington, reawakened after more than a
century of dormancy and provided a dramatic and tragic reminder that
there are active volcanoes in the “lower 48” States as well as in Hawaii
and Alaska. The catastrophic eruption of Mount St. Helens on May 18,
1980, and related mudflows and flooding caused significant loss of life
(57 dead or missing) and property damage (over $1.2 billion). Mount St.
Helens is expected to remain intermittently active for months or years,
possibly even decades.
The word “volcano” comes from the little island of Vulcano in the
Mediterranean Sea off Sicily. Centuries ago, the people living in this
area believed that Vulcano was the chimney of the forge of Vulcan—the
blacksmith of the Roman gods. They thought that the hot lava fragments
and clouds of dust erupting from Vulcano came from Vulcan’s forge as he
beat out thunderbolts for Jupiter, king of the gods, and weapons for
Mars, the god of war. In Polynesia the people attributed eruptive
activity to the beautiful but wrathful Pele, Goddess of Volcanoes,
whenever she was angry or spiteful. Today we know that volcanic
eruptions are not supernatural but can be studied and interpreted by
scientists.