Natural Hazards: Causes and Effects - Disaster Management Center ...

production of sugar and cattle. Because of the fertility of the soil and the tropical climate, the
area was known as Jorullo, which in the language of the Tarascan Indians means “Paradise.”
Near the end of June 1759, the people living at the Hacienda de Jorullo were alarmed by
subterranean noises that, accompanied by mild earthquakes, continued until September 17. At
this time the noises became much louder, being compared to cannonfire, and the earthquakes
were strong enough to seriously damage the chapel. The frightened people fled to the
surrounding hills for safety. At 3:00 A.M. on September 29, about a kilometer to the southeast
of the Hacienda in a ravine known as Cuitinga Creek, a very dark and dense steam cloud rose,
accompanied by sharp earth tremors and loud explosions, and soon flames burst through the
cloud, which was becoming thicker and denser. For two days the volcano threw out masses of
“sand [cinders], fire and thunder without one minute cessation.” On October 1 a mass of “sand
so hot it set fire to whatever it fell upon” rose from the outlet of the volcano, which was little
more than a cleft, and flowed for a kilometer down Cuitinga Creek.
Violent eruptions continued until February 1760, and with decreasing intensity until about 1775,
making the total life of Jorullo’s activity about 15 years. The outpouring of lava consisted of at
least four separate flows, forming a great wasteland that covered nine square kilometers to
depths up to a hundred meters. The flows are believed to have appeared in 1764, considered
to be the year of maximum activity. The first three flows are covered with ash and cinders,
indicating that these materials were still being ejected after the outpourings of lava. However,
the last flow, which issued from a breach on the north rim of the crater and flowed as a great
cascade down the north side of the cone, is free of any ash or cinder cover. This “frozen”
cascade of black lava is still quite “new” and “fresh” looking and is one of the striking features of
Jorullo. It seems likely that this was the end of the explosive activity of the volcano and that
thereafter it was in a venting or fumarolic state.
Jorullo is presently 1,330 meters (4,360 feet) high. The crater is an oval-shaped depression
with a diameter at the rim of 400 meters by 500 meters (1,300 feet by 1,640 feet). Its depth is
150 meters (500 feet) below the highest point. The bottom of the crater appears to have
collapsed since its last eruptive activity, and the bottom is filled with rubble that has fallen from
the sides. At a depth of less than a meter below the rubble the heat is too intense for the hand
but not sufficient to brown a piece of paper or to make water “hiss.” However, the fact that
Jorullo is continuing after 200 years to give off heat as well as gases indicates the life of
volcanoes. 5
Geographical Distribution of Volcanoes
About 500 volcanoes around the world can be considered active, in that they have erupted
during historic times. Many more can be described as dormant: they are not known to have
erupted for thousands of years but could return to activity at any time. For example, Mount
Lamington, in New Guinea, erupted violently in 1951 when it had been thought to be inactive.
Volcanoes are described as extinct when there is no chance of renewed eruption. This is
usually only when a change in the geological environment has effectively defused a once-active
volcano. Over the millions of years of geological history volcanoes have existed in almost every
part of the world and have formed enormous volumes of rock. The entire landmass of Iceland
has been thrown up out of a continuous series of volcanoes. Today volcanoes are generally
found in restricted belts around the world. 6