FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 5 



A line of soundings taken by the fathometer on the Gannet in 1932, ex- 

 tending along an irregular course from a point north of Amukta Pass to 

 Attu Island, at varying distances from the intervening islands, shows 

 that north of the islands the 1,000 fathom line lies close to the island 

 festoon and that at a distance of 50 miles or more from them there is a 

 remarkably smooth-floored depression at a depth of 2,000 to 2,200 fathoms. 

 The shape of this depression between the islands and the continental mass, 

 which includes much of Bering Sea, is not known, but it is significant 

 that the island arc rises as a sharp ridge separating deeps of 2,000 fathoms 

 or more both to the north and south. 



The volcanic nature of this region is well known. Capps (1934, 

 p. 142) says, 



Throughout the Alaska Peninsula the volcanoes have broken out through 

 older sedimentary or igneous rocks, by which they are now flanked. In 

 the Aleutian Islands there are few if any exposures of the basement 

 rocks, and the islands are largely constructional, having been built up 

 to and above sea level by the accumulation of lavas and volcanic fragmental 

 material ejected from below. 



Many volcanoes along this remarkable arc are still in an active 

 state. The eruption of Katmai Volcano, on the Alaska Peninsula, 

 in 1912 was one of the great volcanic spectacles of modem times 

 (see Griggs 1922). The activities of Bogoslof Island and Mount 

 Shishaldin on Unimak Island are well known, and in 1930 there 

 was an eruption on Gareloi Island. On our visit there in 1937 

 we examined some of the small craters, from which were issuing 

 steam and other gases, and. we noted many lava bombs on the 

 lower slopes. We found several typical hot thermal springs that 

 were rimmed with algae. On Kagamil Island, noisy steam jets 

 issued from a rocky bluff, and rumblings could be heard under 

 the boulder beach. After our return from the expedition of 

 1937, we learned that there had been an eruption on Yunaska 

 Island while we had been exploring other areas. Many of the 

 mountains have plumes of steam issuing from the top. Mount 

 Cleveland, on Chuginadak Island, erupted in 1944, and Okmok 

 and Umnak Islands erupted in 1945. 



As would be expected, most of the islands are mountainous. 

 There are a few relatively flat islands, such as Amchitka, Agattu, 

 and Semichi. However, there is a low mountain range along 

 one side of Agattu, and there is a small mountain at one end of 

 Alaid Island, in the Semichis. Most of the larger islands have 

 lakes and streams, and several, such as Amchitka, Agattu, and 

 the Semichis, are dotted with lakes. In keeping with their 

 volcanic origin, some of these islands have notable lava beds that 

 furnish nesting crevices for petrels and auklets, as on Amukta 

 and Gareloi. Other islands, notably Ogliuga and part of Kavalga, 



