Scientific Results of the Katmai Expeditions of the 

 National Geographic Society. 



IV. THE CHARACTER OF THE ERUPTION AS INDICATED 

 BY ITS EFFECTS ON NEARBY VEGETATION.* 



Robert F. Griggs. 



Since the country affected by the eruption of Katmai, in 

 June, 1912, is an uninhabited wilderness, there were no eye- 

 witnesses of the eruption located near enough to give any account 

 of what happened within 25 miles of the volcano. There are, 

 therefore, many features of this, one of the greatest and most 

 interesting of all eruptions, which can never be known except 

 as they are deduced from evidence left behind. Of such 

 evidence that afforded by the effect of the eruption on vegetation 

 is by far the most instructive. 



While the largest value of an examination into the nature of 

 the fate that overtook the plants of the devastated area -lies, 

 perhaps, in its use in interpreting the events of the eruption 

 itself, it has another interest of almost equal importance. It is 

 a necessary prerequisite to the studies of the revegetation of 

 the ash-covered country, which were the primary objects of the 

 Katmai expeditions, because of the manifold bearings of such 

 studies on many problems of the soil relations of plants, both 

 of a theoretical and of a practical nature. We shall combine 

 these two interests in this paper, giving not only such data as 

 contribute to an understanding of the eruption, but also 

 discussing the restorative reactions of the surviving plants so 

 as to form a basis for the papers on revegetation which are 

 to follow. 



THE ZONES OF DAMAGE. 



As marked by the extent of injury to vegetation, the country 

 affected by the eruption may be divided into several zones of 

 damage. In the outermost zone the plants suffered from acid 

 rains, but the ashfall was so light as to do no damage of conse- 



* Copyright, 1919, by National Geographic Society, Washington, D. C. All 



rights reserved. 



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