PART II— DYNAMICS OF THE SOLID EARTH 



been found commonly. In retrospect, 

 workers at Nyamuragira Volcano, in 

 central Africa, believed that swarms 

 of earthquakes would have made it 

 possible to predict the 1958 eruption 

 about 30 hours before the outbreak, 

 but no such prediction was made. At 

 most volcanoes, including most of 

 those in western United States, the 

 instrumental installations necessary to 



recognize either earthquake preludes 

 or diagnostic tilt patterns are still 

 lacking. 



History — The prediction of the 

 type of eruption rests almost wholly 

 on a knowledge of the past history of 

 the volcano. What has happened be- 

 fore is most likely to happen again. 

 In most instances, however, the his- 



tory must be deduced from careful 

 geological studies, and we still do not 

 know the history of most of the 

 earth's volcanoes. 



Clearly, it will be some time before 

 we can consistently predict eruptions 

 at most volcanoes, including those in 

 some of the most heavily populated 

 areas. 



Aspects of Volcanic Science 



Giant strides have been made in 

 our understanding of the dynamics 

 of the earth's surface and of the be- 

 havior of rock systems at pressures 

 and temperatures equivalent to sub- 

 crustal conditions within the earth. 

 Yet our knowledge of the basic 

 physics and mechanisms involved in 

 volcanic processes are at best sketchy, 

 our explanations speculative and 

 largely qualitative, and our predic- 

 tions based on observed history rather 

 than fundamental understanding of 

 the real mechanics involved. 



The number of scientists conduct- 

 ing serious investigations of volcanoes 

 is fairly small; they are concentrated 

 in the countries where most of the 

 earth's 450 active volcanoes are 

 found — the circum-Pacific belt (New 

 Zealand, the Philippines, Japan, east- 

 ern Soviet Union, Alaska, and western 

 North and South America) and an 

 east-west region extending from Java 

 through the Mediterranean. Most of 

 today's students are Japanese, Ameri- 

 can, Russian, Italian, Australian, In- 

 donesian, or Dutch. 



Interaction with Man and 

 Environment 



Volcanoes are spectacular in state 

 of eruption, and their effects on life 

 and property have often been devas- 

 tating. Damage is inflicted by several 

 means: fall of fine-grained ash from 



the atmosphere; ash flows; lava flows; 

 and tidal waves associated with 

 violent eruptions. The most devas- 

 tating and dangerous eruptions are 

 those that produce ash flows or vio- 

 lent blasts. These are also among the 

 least understood, because the erup- 

 tions are short-lived and have not 

 been well studied. 



The United States has over 30 

 active volcanoes, mostly in Alaska. 

 (See Figure II-8) Within continental 

 United States, large dormant vol- 

 canoes include Mt. Rainier, Mt. Baker, 

 Mt. St. Helens, Mt. Shasta, and Mt. 

 Lassen. Phreatic (steam-blast) erup- 

 tions occurred in Hawaii in 1924; the 

 hazard grows with population density. 



Alteration of the environment near 

 an erupting volcano can be dramatic. 

 Some believe the decline of Minoan 

 civilization on Crete (about 1500 B.C.) 

 resulted from the eruption of the vol- 

 cano Thera. More recently, an ash 

 fall associated with the 1968 eruption 

 of Cerra Negro, Costa Rica, threat- 

 ened to choke off San Juan, the capital 

 city. In the United States, historic 

 lava flows from Kilauea and Mauna 

 Loa, on Hawaii, have reached the sea, 

 burying productive sugar cane fields. 

 The 1959 flow accompanying an erup- 

 tion along the east rift zone of Kilauea 

 buried the town of Kapoho. The 1950 

 flow from Mauna Loa reached the sea, 

 endangering for a time the town of 



Kailua-Kona on the west side of 

 Hawaii. 



Among the greatest direct threats 

 to life are eruptions producing ash 

 flows. A spectacular and devasting 

 historic eruption of this type occurred 

 on Martinique in 1902. An ash erup- 

 tion from Mt. Pelee flowed down the 

 flank of the mountain at an estimated 

 50 to 100 miles per hour and buried 

 the town of St. Pierre, with a loss of 

 38,000 lives. A passing ship observed 

 a similar eruption at Mt. Katmai, 

 Alaska, in 1912; it produced the Val- 

 ley of Ten Thousand Smokes, but 

 there was no known loss of life. Such 

 eruptions could recur nearly any- 

 where along the Aleutian chain. An 

 eruption of this type in a populated 

 region would be a catastrophe. 



One of the most dramatic examples 

 of the effect of volcanic action on the 

 environment was the eruption of 

 Krakatoa, in 1883, in eastern Sumatra. 

 Krakatoa is a large, cauldron-type 

 volcano. It erupted with an energy 

 estimated as equivalent to 100 to 150 

 megatons of TNT. Some 36,000 peo- 

 ple lost their lives in this eruption and 

 the tidal wave that accompanied it. 

 The blast was believed to have been 

 the result of sea water entering the 

 magma chamber after a two-week 

 period of relative quiet. The resulting 

 acoustic wave produced in the atmos- 

 phere propagated to the antipodes 



44 



