VOLCANOES 



of Hawaii have covered more than 

 300 square miles of land surface. 

 Much of this was unused land on the 

 upper slopes of the mountains, but in 

 1955 a large part of the six square 

 miles buried by lava was prime agri- 

 cultural land. Again in 1960, several 

 hundred acres of rich sugar land were 

 covered. On the other hand, the lava 

 built out the shoreline of the island, 

 creating half a square mile of new 

 land. 



The land buried by lava flows is not 

 lost forever. The rapidity with which 

 vegetation reoccupies the lava surface 

 varies greatly with climate. In warm 

 areas of high rainfall, plants move in 

 quickly. The lava flows of 1840, on 

 the eastern end of the island of 

 Hawaii, are already heavily vegetated. 

 In dry or cold areas the recovery is 

 much less rapid. 



It has been found that simply 

 crushing the surface of the lava, as by 

 running bulldozers over it, greatly 

 speeds reoccupation by plants, appar- 

 ently because the crushed fine mate- 

 rial retains moisture. Certain types of 

 plants can be successfully planted on 

 a surface treated in this way within a 

 few years of the end of the eruption. 

 In 1840, Hawaiians were found grow- 

 ing sweet potatoes on the surface of 

 a lava flow only about seven months 

 old. Experimentation with ways of 

 treating the flow surface and with 

 various types of plants will probably 

 make it possible to use many flow 

 surfaces for food crops within two 

 years of the end of the eruption. 



Methods for the Diversion of Lava 

 Flows — Several methods have been 

 suggested. In 1935 and 1942, lava 

 flows of Mauna Loa, Hawaii, were 

 bombed in an effort to slow the ad- 

 vance of the flow front toward the 

 city of Hilo. The results indicated 

 that, under favorable circumstances, 

 the method could be successful. They 

 also indicated, however, that not all 

 lava flows could be bombed with use- 

 ful results. 



It has been suggested that lava 

 flows can be diverted by means of 

 high, strong walls, not in order to 

 stop the flow but only to alter its 

 course. Walls of this sort, although 

 poorly planned and hastily built, were 

 successful to a limited degree during 

 the 1955 eruption. Walls built during 

 the 1960 eruption were of a different 

 sort, designed to confine the lava 

 like dams rather than to divert it. 

 Although the lava eventually over- 

 topped them, they appear to have 

 considerably reduced the area de- 

 stroyed and were probably respon- 

 sible for the survival of a large part 

 of a beach community and a vitally 

 important lighthouse. 



Whether such walls would be effec- 

 tive against the thicker, more viscous 

 lava flows of continental volcanoes is 

 not known. Thick, slow-moving lava 

 flows at Paricutin Volcano, in Mexico, 

 did not crush the masonry walls of a 

 church that was buried by the lava 

 to roof level. Walls generally would 

 be useless against lava of any vis- 

 cosity where the flow is following a 

 well-defined valley. Fortunately, the 

 flows of continental volcanoes usually 

 are shorter and cover less area than 

 Hawaiian flows, thus reducing the 

 area of risk. Much more research is 

 needed on ways to control lava flows. 



Ash Falls 



It was formerly believed that ash 

 from the great explosion of Krakatoa 

 Volcano, between Java and Sumatra, 

 drifted around the earth three times 

 high in the stratosphere. Although it 

 now appears that the brilliant sunsets 

 once regarded as evidence of this were 

 probably caused instead by an aerosol 

 of sulfates resulting from interaction 

 of volcanic sulfur dioxide gas and 

 ozone, it has been repeatedly demon- 

 strated that violent eruptions may 

 throw volcanic ash high into the 

 upper atmosphere, where it may drift 

 for hundreds of miles. For instance, 

 ash from the 1947 eruption of Hekla, 

 in Iceland, fell as far away as Mos- 



cow; ash from the eruption of Qui- 

 zapu, in Chile, fell at least as far away 

 as Rio de Janeiro, 1,850 miles from 

 the volcano; and ash from the Crater 

 Lake eruption has been traced as far 

 as central Alberta. 



Although it has not been absolutely 

 proved, it appears probable that large 

 amounts of ash in the atmosphere 

 affect the earth's climate. Ash from 

 the 1912 eruption of Mt. Katmai, 

 Alaska, is believed to have reduced by 

 about 20 percent the amount of solar 

 radiation reaching the earth's surface 

 at Mt. Wilson, in southern California, 

 during subsequent months; ash from 

 the Laki eruption in Iceland drifted 

 over Europe and appears to have 

 caused the abnormally cold winter of 

 1783-84. Other examples have been 

 cited, although some investigators 

 find no evidence for it. 



Heavy ash falls may destroy vege- 

 tation, including crops, within a radius 

 of several miles around the volcano. 

 Ash from the Katmai eruption de- 

 stroyed small vegetation at Kodiak, 

 100 miles away, although bigger trees 

 survived. During the 1943 eruption 

 of Paricutin, even the big trees were 

 killed where the ash was more than 

 three feet deep. Even a few inches of 

 ash will smother grass. 



Serious indirect consequences may 

 arise. A great famine that resulted 

 from destruction of vegetation and re- 

 duction of visibility to the point 

 where the fishing fleet could not work 

 followed the Laki eruption and is said 

 to have killed a large proportion of 

 the population of Iceland. Around 

 Paricutin, thousands of cattle and 

 horses died, partly of starvation and 

 partly from clogging of their digestive 

 systems from eating ash-laden vege- 

 tation. Even if it causes nothing 

 worse, ash-covered vegetation may 

 cause serious abrasion of the teeth of 

 grazing animals. Cane borers did 

 serious damage to sugar cane in the 

 area west of Paricutin, because the 

 ash had destroyed another insect that 

 normally preyed on the borers. Any 



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