50 C. H. HITCHCOCK VOLCANIC PHKNOMEXA ON HAWAII 



been distinctly struck in the face by particles of the volcanic dust. 

 July 17 the steamer '' Mariposa " observed this smoke, some 600 miles 

 to the northeast. Similar! v the officers of the " Morning Star " found 

 themselves unable to take the customary observations for latitude at an 

 equally great distance to the southwest. The diameter of the area ob- 

 scured must have considerally exceeded 1,200 miles, as the observations 

 reported were much to the north of the major axis. 



It was also interesting to observe the presence of an enormous cumulus 

 cloud directly over the crater of Mokuaweoweo. This was developed by 

 the rising of heated vapors from the summit crater coming in contact 

 with a cooler atmosphere. 



Mokuaweoweo 



Plate 5 is copied from photographs taken by Davey of the appearance 

 of the pit Mokuaweoweo Jul}^ 13. Concerning the appearances Professor 

 Ingalls writes : 



" The floor of the crater was of black lava, to all appearance precisely like that 

 of Kilauea, with a few roiij^h patches here and there which I })elieve was 'aa.' 

 Extending in a direction roughly parallel with the west wall, from the talus at the 

 base of the lower terrace at the north pretty nearly to the gap in the south, there 

 stretched a crack in the crater floor, all points of which lay slightly west of the 

 medial north-and-south axis. From various places along tiiis fissure rose up nearly 

 all the signs of the existence of volcanic fires beneath, these evidences being sickly 

 jets of steam, rising in such a manner as to suggest no urgency from below ; also 

 at the bottom of the southwest wall the talus appears to be undergoing a trans- 

 formation into sulphur banks. There was nothing in the appearance of this summit 

 crater to warrant an assumption that at this very time, at the depth of 3,000 to 

 3,500 feet below the level of this floor, there was a genuine volcano in terrific 

 eruption."* 



Two Kinds of Ekuptions 



The history of volcanic action on Mauna Loa indicates two kinds of 

 era[)tion. Most of them have presented phenomena of this nature: 

 After pretnonitory earthquakes, the first manifestation of activity is the 

 sudden appearance of much molten lava in the top crater, Mokuaweoweo, 

 which is shown by the light reflected on the sky. Often the finest foun- 

 tains of fire are displayed at the summit. Within a very few days there 

 is a fracture in the side of the mountain, accompanied by noise, and 

 lava flows freely, as if from h3alrostatic pressure, and the liquid disaj)- 

 pears at the summit. So far as known, all the discharges from altitudes 

 of 4,000 feet or less below the surface of the fused lava have made their 



* Hawaiian Annual for 1900. 



