134 Washington — Submarine Eruptions of 1831 and 1891. 



July 8 the surface of the sea was seen to rise to a height of. 80 

 feet, the column maintaining itself for ten minutes, and then 

 again sinking down. This was repeated every quarter to half 

 an hour, and was accompanied by a dense cloud of black smoke 

 and loud rumblings. This column of smoke increased rapidly, 

 and by the 12th large quantities of light-colored pumice were 

 w T ashed up on the beach at Sciacca. This material was ana- 

 lyzed by Abich. 



On the 16th, Giovanni Corrao saw at the base of the column 

 a small island about 12 feet high with a crater in its center 

 containing boiling red water. The island increased rapidly in 

 size, and was visited by Professors Hoffmann and Esscher. 

 They estimated its height at about 60 feet and its diameter at 

 800 feet, though they do not appear to have landed. At this 

 time the island had the form of a crescentic cone, with an 

 opening to the sea on its southwest side, while a column of 

 white smoke rose to an estimated height of 2000 feet. 



A landing was first effected on Aug. 2, by Capt. Senhouse, 

 who took possession of it for the British crown and gave it the 

 name of Graham Island. After this it was visited by several 

 geologists and others: by Gemrnellaro on Aug. 12; by Hoff- 

 mann on Sept. 26, and by Prevost on Sept. 29. 



The volcano seems to have attained its greatest dimensions 

 of 65 meters high, with a circumference of about 3700 meters, 

 in the early part of August, after which volcanic activity 

 gradually diminished, though an eruption took place sonthwest 

 of the island during this month. The general form was that 

 of the summit of a cinder cone, the ridge being of uneven 

 height, with a crater containing water in the center. The 

 form changed materially from time to time, partly through the 

 accumulation of volcanic ejections and partly through the 

 destructive action of the sea, and the crater was sometimes 

 breached and open to the north, and again to the south. But 

 the sketches made of it are rather crude and unsatisfactory, 

 for the most part. Among the best are those reproduced from 

 drawings by Wright, given by Mercalli.* 



The material of which the cone was built up is unanimously 

 stated to be volcanic sand, lapilli, and scoriae, arranged in 

 strata partly dipping inward toward the crater and partly dip- 

 ping outward on the outer portions. The absence of lava flows 

 is expressly noted by nearly all the observers. Although the 

 material Avas undoubtedly to a large extent scoriaceous and 

 fragmentary, yet the peculiar forms shown in some of the 

 sketches lead to the inference that there was involved in the 

 structure an upthrust of lava, probably in a highly viscous con- 

 dition and more or less broken at the top. That is, there was 

 probably present an upthrust plug or spine somewhat resem- 



* Vulc. Ital., plates viii and ix. 



