J. D. Dana — Eruptions of Kilauea and Mt. Loa. 99 



of the stream of 1880-81, near Hilo, which I visited under the 

 guidance of Kev. E. P. Baker, one of the lines of mouldings 

 had the form and position along the side of a solid handsomely 

 modeled bench, indicating that the lava had encountered an out- 

 side obstacle in a projecting angle of cooled rock. This tunnel 

 had a varying height of 4 to 8 feet and a general width of about 

 30 feet, but also some branchings and lateral expansions of large 

 extent. The roof was two to six feet thick. The smoothness 

 of the interior is favorable to a high velocity. The small ca- 

 pacity of the one entered near Hilo suggested the following 

 queries : How much of the lava of a stream a mile wide runs 

 in tunnels ? Does the little width of the tunnel, and thereby 

 of the supply stream, account for the difference of velocity in 

 the tunnels and at the front ? if so, the exit should be as free as 

 that from a faucet, or the arrangements would not work. How 

 many such tunnels exist side by side % Does a single tunnel 

 continue on for 20 or 30 miles as an uninterrupted lava duct ? 

 "We should infer that for a large stream the system of tunnels 

 would become a very complicated one. 



Whatever doubts exist as to rate of flow, there is none as to 

 the extreme liquidity of the Mt. Loa lava, and its equalling if 

 not exceeding that of Kilauea. 



3. The amount of Lava discharged. — There are no data as 

 regards the breadth or the depth of the streams, for a satisfac- 

 tory calculation of the amount discharged. The depths might 

 at many points be ascertained from the holes left by burnt 

 trunks of trees. We can now only make a supposition. 



The flow of 1852 was 20 miles long. If we suppose- the mean 

 depth of the stream to be 20 feet, and the mean width, 5000 

 feet, the amount of lava it contains would be 10,560,000,000 

 cubic feet. Supposing the lava -column to have the mean di- 

 ameter of the central part of the summit crater, 9000 feet, it 

 would contain, down to a depth of 2500 feet, (the place of dis- 

 charge for that eruption) nearly 160,000,000,000 cubic feet of 

 lava, or fifteen times as much as was discharged. Accordingly, 

 the discharge, if the above figures represent the whole amount, 

 would have drawn off less than 200 feet in depth from the lava 

 conduit ; and a rise of 200 feet again would have made the 

 mountain ready for another discharge. The calculation is sug- 

 gestive, though otherwise of little value. In addition to the 

 other uncertainties we know nothing as to how much of a dis- 

 charge passes off into subterranean cavities ; which may be very 

 large, for the great eruption of Kilauea in 1832 has little to 

 show over the surface of the island. 



Whatever the amount of lava or of height that is lost by the 

 lava-column at an eruption, it has taken, as has been shown, but a 

 very short time in several cases, to fill up again for a new dis- 



