Haedcastle. — On the Tarawem Eruption. 277 



Art. XXXVII.— The Tarawem Eruption, 10th June, 1886— .4 

 Criticism of Professor Hutton' s (and others' J Explanations 

 of the Causes of the Eruption. 



By J. Haedcastle. 



[Read before the Hawke's Bay Philosophical Institute, 8th June, 1887.] 



A report has been published by Professor Hutton, F.G.S., on 

 the Tarawera Volcanic District in which he gives the conclusions 

 he arrives at, after a visit to the locality and a study of a sub- 

 dued phase of activity, as to the causes of the eruption in June, 

 1886. Those conclusions, it is to be inferred from a foot-note 

 to page 12 of the report, are concurred in by Professors Thomas 

 and Brown. 



The explanation given of the cause of the eruption appears 

 to me so much at variance with the probabilities of the case, as 

 to invite criticism, especially as the general theory of volcanic 

 action is involved. (See Pieport, pp. 14 to 18.) 



Undoubtedly Professor Hutton is right in concluding that 

 " the cause was local," — " in the mountain," he says, italicising 

 these words ; " beneath the mountain " would surely be more 

 correct, according to his own explanation. He is right, also, in 

 saying that the heat "could not have been caused by upward 

 conduction, through the solid crust, of the internal heat of the 

 earth." Undoubtedly right also in concluding that " no chemical 

 changes, at all competent to do the work, suggest themselves as 

 the cause of the re-heating of the surface rocks." Having put 

 aside these as incompetent causes, he mentions two others : the 

 production of heat by (1) the crushing of rocks, and (2) the rise 

 of a quantity of molten rock from somewhere in the depths of 

 the earth. The first of these he dismisses after a very imperfect 

 examination, as " very improbable ;" the second he accepts as 

 the true cause, though he shows that both the alternative modes 

 by which it is suggested such uprise of molten rock might be 

 brought about are open to objection, and makes no attempt to 

 answer the objections to either, and expressly declines to choose 

 between them. 



I propose to show that the explanation put aside as "very 

 improbable " is the most probable, and the true cause, and that 

 an uprise of molten rock is very improbable. 



In the first place, there is no evidence of an uprise of molten 

 rock at all, in such quantity as would be necessary to re-heat all 

 the rock that was ejected, and to vaporise all the water which, 

 as steam, supplied the ejecting power. Professor Hutton finds 

 such evidence in the earthquakes which for some months pre- 

 ceded the eruption. These, however, were in no way remark- 

 able, and they afford no evidence as to their cause. Such an 

 addition, as that supposed, to the mass of the crust beneath 



