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Gareloi reported activity




Start:April 1929 Observed
Stop: 1930 Observed

Lava flow: BibCard BibCard
Tephrafall: BibCard
Debris-avalanche, volcanic avalanche, or landslide: BibCard
Directed blast: BibCard
Steam: BibCard BibCard
Tephra plume: BibCard
Radial fissure: BibCard BibCard
Phreatic: BibCard BibCard BibCard
Eruption Type:Explosive
MaxVEI: 3 BibCard
Eruption Product: andesite BibCard

Description: Coombs and others (2008) provide information about the 1929 eruption as follows: "The 1929 eruption is the largest historical eruption of Gareloi and also unique in its eruptive style and composition. The most detailed description of the eruption is given by oats (1959) who summarized the first-hand observations of William H. Dirks, Sr. (Coats, 1959; p. 2): 'In April of 1929, there was an eruption. A terrible quake * * * split the mountain from its crater right to the beach. Ashes fell, completely covering their cabins and boats* * * '

"Coats further elaborated on the series of events from observations of the deposits, which were 17 years old when he visited the island and still unmodified either by vegetation or further eruptive activity. According to Coats, the eruption excavated 13 explosion craters, ranging in diameter from 80 to 1,600 m, along a 4.3-km-long, south-southeast trending fissure [see figs. 5 and 7 in original text]. On the basis of work by Coats (1959) and our fieldwork, the eruption began with formation of the current South Peak crater and a possible directed blast to the south. Following this, an explosive eruption covered the southern half of the island in several meters of tephra fall [see fig. 8 in original text]. At this time, the upper craters were excavated. Small pyroclastic flow deposits are interbedded with tephra-fall deposits, indicating that pyroclastic flows accompanied tephra fall.

"During the second half of the eruption, the composition of the juvenile clasts in the fall deposits became more mafic; craters formed lower on the flank, and small lava flows effused from them. Sometime after explosive activity ceased, debris flows from the summit carried hydrothermally altered blocks down the volcano's southern slope.

"The eruption's total volume is unknown, as much of the ejecta were deposited offshore. Onland pyroclastic deposits represent about 16,000 cubic m, and that of lava is about 2,500 cubic m."

Miller and others (1998), also summarize Coats (1956): "In April of 1929, a phreatic eruption opened an elongate crater 1600 m in maximum diameter just below the southern summit; further explosions produced 12 smaller craters aligned along a south- to southeast-trending fissure. Glassy pumice, lapilli, scoria, and accidental rocks were then ejected from the lower craters, blanketing an area roughly 2.5 by 5 km on the southeast slope. Ash layers up to 2 m thick on Ogliuga Island, located about 16 km southeast, may be attributable at least in part to this eruption (Coats, 1956, p. 92) and several centimeters of pyroclastic debris are known to have fallen on Atka Island (about 300 km eastward) during the event. Extrusion of lava, which formed short steep flows, occurred at four sites along the fissure after the tephra eruptions. Various metallic oxides and halides (including atacamite, paratacamite and hematite) were deposited in several of the lower craters. Activity may have continued into 1930.

"Juvenile material erupted in 1929 may be significantly more siliceous than the older basaltic or basaltic andesite rocks. The lava was apparently highly viscous and generally formed blocky, vesicular, or scoriaceous flows, one of which is 75 m wide and 15 m thick. Orthopyroxene, brown hornblende, plagioclase (average composition about An48), and clinopyroxene were observed in lava flows and pyroclastics of the 1929 eruption (Coats, 1959, p. 254-255)."

Finch (1931): "Gareloi volcano, a peak 5,334 feet high far to the west in the Aleutian Islands, was very active during the spring and summer of 1930. The appearance of half of the island was said to be changed by lava flows from fissures, and a hut was destroyed belonging to fox farmers."

Jaggar (1932): "Gareloi in the western Aleutians was said to erupt so violently in 1930 as to change its appearance by lava flows from fissures."

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