The Tarawera Outbreak. 123 



chasm lias an effect which corresponds to that of the leak in 

 the locomotive boiler, or to that of the rupture of an aneurism 

 in some great artery. It provides the lava with such an 

 extent of free surface that its steam escaped without effective 

 effort — that is, without accumulating anywhere hydrostatic 

 pressure enough to lift the lava over the lip. Thus the 

 pumping-up power is lost, and only lava bubbles escape, and 

 these, saturated with high-tension steam, explode into dust 

 at the moment of complete relief 



It will be seen, therefore, that the size of the rupture fully 

 accounts for the absence of a lava flow, and is the key to the 

 character of the outbreak. 



Tarawera will become notable because it is an example 

 of the comparatively rare fissure-type of eruption, instead 

 of being one of the familiar cone-and-crater type. 



It is now believed that every volcano has commenced as a 

 fissure. The fissure is sealed up when the first great steam 

 escape has ceased, excepting at one or two points where 

 small cones form and let off the residue, and then become 

 plugged up in their turn. In time steam accumulates again, 

 and ultimately a second phase of eruptivity commences. In 

 this revival of activity the fissure does not reopen, but only 

 the cones, which this time erupt lava and ash, and grow 

 rapidly in size, so that in time the old fissure is buried under 

 either a chain of small craters or under one large volcano. 

 Whether or no such a development as this is to be the sequel 

 of Tarawera only the future can tell us. 



The meteorological conditions which accompanied the 

 eruption are hardly referred to in the official reports. 



From other sources we gather the interesting fact that it 

 occurred at a time when an area of barometrical depression 

 passed over that end of New Zealand. Mr. Cheeseman, the 

 Government Meteorologist, states that at 4 a.m. on June 

 9th the barometer stood at 30'27, but that it then fell until 

 it touched 29*94, or a drop of one-third of an inch, at which 

 it stood until 4 a.m. of the 10th, the morning of the out- 

 break, when it began to rise again. 



Unfortunately, we have no barometrical readings from the 

 immediate neighbourhood of the disturbance, but the New 

 Zealand papers give a singular story, which points to a 

 heavy fall at Wairoa. It is stated that during the bitterly 

 cold morning when the eruption was at its climax, some of 

 M'Rae's party lit a fire to make a drink of cocoa, but that at 

 the end of three-quarters of an hour, and although the water 



