Brevity of Tuff-Cone Eruptions. — Bishop. 5 
lent to a theoretical hight of only 1,900 feet of projection aloft. 
It is evident that this is totally inadequate.- Assume then only 
two hours' duration of the eruption. This gives us 875 feet of 
velocity of emission, equivalent to a hight of projection of 
11,925 feet. Such an altitude of the fountain might be ade- 
quate to the actual distribution of the ejecta to an average dis- 
tance of 2,500 feet from the vent. But it must be noted that 
the hight attained with the assumed velocity could hardly be 
more than two-thirds of the theoretical one, on account of the 
resistance from the falling tuff encountered by the ascending 
jet. It is also evident that the fountain must have been a 
very lofty one for the tuft" to have been driven half a mile to the 
leeward by even a heavy gale, as so much of it was done in 
building up the massive cone. 
The real area of the vent can be less accurately estimated. 
The partially exposed vent of the neighboring crater of Punch 
Bowl is apparently fully a hundred feet in diameter. The 
only completely open vent of the kind which I have seen is that 
of.Kalaupapa at the leper settlement on Molokai. This is a 
rocky well with vertical sides reaching down to salt water, 
which is 800 feet deep. The diameter of this well or shaft 
was, as I remember it, from 100 to 150 feet. Guided by these 
data I should consider 5,000 square feet as a very conservative 
estimate for the sectional area of the shaft from which issued 
the tuff of Diamond Head, instead of the 2,000 feet assumed 
above Such increased area would reduce the two hours' dura- 
tion assumed, to 48 minutes. It would be much less if we 
allow a greater velocity of ejection, so as to get a hight of the 
fountain adaquate to allow of its extensive deflection by wind. 
I incline to the belief that the eruption did not last more than 
half an hour. It is absolutely impossible that it could have 
continued many hours. 
These explosive eruptions are of gigantic force and brief 
duration. 
Honolnin, November 14//?, 1900. 
