VOLCANOES 



Figure 11-8— U.S. VOLCANOES 



CANADA 



Mt. SI. Helen 



Ml R ji 



Mt Hood ," Ml, Adams YX 



Mt Jefferson # « / / Columbia River 



Crato'lake •** "-' \ p| a'M" 



Mt. Shasta t 

 / 

 Lassen Peak a 



This figure indicates the active volca- 

 noes of the U.S. as well as Quaternary 

 volcanoes and other areas of volcanic 

 activity. 



and back eight times as recorded by 

 microbarographs around the world. 

 Fine-grained ash was dispersed 

 throughout the atmosphere and pro- 

 duced distinctly red sunsets as far 

 away as Europe. 



Long-Term Effects — Volcanoes 

 may also have an important effect on 

 man's environment on geologically 

 long time-scales. Fine-grained air- 

 borne volcanic material may have a 

 serious effect on the long-term heat 

 balance of the earth, for example, by 

 changing the reflection properties of 

 the upper atmosphere. The ash from 

 Krakatoa reduced the incident solar 

 flux to the surface by about 20 per- 

 cent of its normal value. Such effects 

 have been postulated as a possible 

 contributing cause for continental 

 glaciation. In this view, glaciations 

 result from a reduced heat flux to the 

 earth's suface as a consequence of 

 fine ash in the atmosphere dispersed 

 by a higher general level of volcanic 

 activity. 



In addition, most of the gases that 

 produce the atmospheres and oceans, 

 the products of outgassing of the 

 earth's interior, probably reach the 

 surface through volcanoes. Hence, 

 the nature of volcanism is intimately 

 tied to such general questions as the 

 nature and evolution of planetary 

 atmospheres. 



Ability to Forecast Eruptions 



Perhaps the most serious matter is 

 that of predicting catastrophic and 

 unexpected eruptions. Volcanic soils 

 are among the most fertile in the 

 world; consequently, the slopes of 

 even active volcanoes are populated 

 and used for agricultural purposes. 

 Furthermore, the time between violent 

 volcanic events varies from several 

 decades to several thousand years — a 

 short time geologically but a long time 

 on the scale of man's life and memory. 

 There is thus a significant amount of 

 economic pressure to occupy hazard- 

 ous places. It is virtually certain that 

 violent eruptions like those at Kraka- 

 toa, Vesuvius, or Mt. Pelee will occur 

 in the future. 



Our ability to explain or predict 

 volcano behavior is poor and restricted 

 to a few isolated, well-studied ex- 



amples. The behavior of Kilauea, on 

 the island of Hawaii, is one of the 

 most systematically monitored and 

 historically well-studied volcanoes in 

 the world, along with Asama and 

 Sukurajima in Japan. (In 1914, Su- 

 kurajima erupted and seven villages 

 were destroyed; property damage was 

 some $19 million, as 25 square kilo- 

 meters were buried under new lava; 

 no lives were lost.) Kilauea has been 

 monitored almost continuously since 

 1912, the year that Jagger estab- 

 lished the Hawaiian Volcano Obser- 

 vatory (HVO), operated since 1917 by 

 the U.S. Geological Survey (USGS). 

 Integrated geological, geophysical, 

 and petrological chemical observa- 

 tions have been made of Kilauea's 

 eruptions and the lavas produced. 

 Small-scale earthquakes accompany- 

 ing upward movement of molten rock 

 at depth have also been studied. 

 Swelling of the volcano prior to erup- 

 tion has been monitored by precise 

 leveling and strain measurements. All 

 this has resulted in a basis for erup- 

 tion prediction based on previous ex- 

 perience. 



The ability to predict eruptions at 

 Kilauea has little use elsewhere, how- 

 ever, since each volcano has it own 

 personality which must be studied to 

 be understood. Furthermore, Hawai- 

 ian-type volcanism, while it has been 

 destructive of property, is the most 

 passive of all types of eruption. And, 

 in spite of a long history of observa- 

 tion and systematic data collection at 

 Hawaii, we are still basically ignorant 

 of some important and interesting 

 facts: details of the melting processes 

 operative in the earth's mantle that 

 are responsible for the generation of 

 the lava; the mechanics of the propa- 

 gation of fractures in the mantle crust 

 and the hydrodynamics of transport 

 of the lava to the surface; the rela- 

 tionship of the lava to the fragments 

 of subcrustal (mantle) rocks contained 

 in some lavas; the nature of the man- 

 tle underlying Hawaii; and, finally, 

 why the Hawaiian chain (and the ac- 

 tive volcanism) is marching south- 

 eastward across the Pacific. 



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