Jan., 1919] Effects of the Eruption on Vegetation 191- 



FALLING ASH RELATIVELY COOL. 



The testimony of such plants shows that the explosion of 

 Katmai differed markedly from many eruptions in the low 

 temperature of the ejecta. In the case of Tarawera, for example, 

 Pond and Smith 6 report that the ejecta retained a high tem- 

 perature for a considerable time after they had fallen, and that 

 the forest was consumed by fires, started presumably by the 

 hot ash. If such conditions had accompanied the explosion of 

 Katmai the evidence of them would be plain today. But 

 nowhere is there any evidence of fire, neither charred wood 

 nor indications that the buried trees and bushes were injured 

 by the heat of ejecta coming from Katmai itself. On the con- 

 trary, wood of the buried bushes everywhere throughout this 

 zone, even high up on the slopes of the volcano itself, is sound 

 and well seasoned as though kiln dried. 



The survival of the buried plants is even more significant 

 evidence of the condition of the falling ash. Had the ejecta 

 been hot as they fell, the deeper deposits would have cooled 

 off very slowly and almost certainly would have cooked the 

 plants beneath. The survival of plants under coverings up to 

 15 feet in depth would seem to demonstrate conclusively that 

 the deposits could never have had a very high temperature. 



Over large areas the ash fell on snowdrifts which, instead 

 of being melted as they would have been by hot ejecta, were 

 insulated by the thick mantle of ash and have persisted until 

 the present time. The picture on page 190 shows a cavern 

 caused by local melting of such a snowdrift which remained 

 unchanged for five years after the eruption. The strata of ash 

 lie as smoothly over the snow as over the bare ground, and 

 there is not the least indication of irregularities due to superficial 

 melting caused by the heat from the ejecta. 



The low temperature of the ash is probably connected with 

 the character of the ejecta, which are composed of exceptionally 

 small fragments. There were no bombs of solid lava nor even 

 large pieces of pumice thrown out from Katmai itself. All the 

 ejecta are the type of frothy pumice and the largest lumps 

 seldom reach ten inches in diameter. The finely fragmental 

 character of the ejecta would operate in two ways to reduce the 



6 Pond and Smith. On the Eruption of Mt. Tarawera. Trans. New Zealand 

 Institute, 19 : 362 ; 1886. 



