August 29, 1878 Eruption of Okmok

Reference #1686:

"Other tsunamis due to earthquakes accompanying eruptions: - 1878 August 29 Okmok?"

Reference #10691:

From Grey (2003): "A new crater is reported to have formed within the caldera in 1878 (Hantke, 1951), accompanied by earthquakes and a tsunami (location unknown). This could refer to the birth of Cone A, but since Hantke offers no additional information or references to support this notion, the report is apocryphal at best. It is intriguing to note that eruptions are also reported at Vsevidof, on the southwestern end of Umnak Island, in 1817, 1830, and 1878 (Miller et al., 1998). Of particular interest is the suggestion by Miller et al. that the 1878 activity of Vsevidof 'may have been from a radial fissure eruption on the west flank; this event may have produced the youngest dacite flow, which extends west-southwest to Cape Kigushimkada.' Such a fissure eruption would probably produce earthquakes and could account for Hantke's 'new crater,' though not located inside a caldera. It is thus possible that Hantke misinterpreted the location of the 1878 activity, and there may not have been an eruption at Okmok in that year at all."

Sapper (1917), compiling information from Petroff (1884) and Fuchs, reports "a brief flame and ash eruption and a new crater developed from which came steam and hot cooking mud. This new crater appeared between Vsevidof and the settlement." This statement seems to support Miller et al.'s (1998) assertion that there was a radial fissure eruption at Vsevidof in 1878.

Reference #2432:

Confirmed eruption of Okmok in 1878. VEI: 2. The broad, basaltic Okmok shield volcano, which forms the NE end of Umnak Island, has a dramatically different profile than most other Aleutian volcanoes. The summit of the low, 35-km-wide volcano is cut by two overlapping 10-km-wide calderas formed during eruptions about 12,000 and 2050 years ago that produced dacitic pyroclastic flows that reached the coast. More than 60 tephra layers from Okmok have been found overlying the 12,000-year-old caldera-forming tephra layer. Numerous satellitic cones and lava domes dot the flanks of the volcano down to the coast, including 1253-m Mount Tulik on the SE flank, which is almost 200 m higher than the caldera rim.

Some of the post-caldera cones show evidence of wave-cut lake terraces; the more recent cones, some of which have been active historically, were formed after the caldera lake, once 150 m deep, disappeared. Hot springs and fumaroles are found within the caldera. Historical eruptions have occurred since 1805 from cinder cones within the caldera.

Reference #3789:

Historic accounts of the 1878 event do not clearly document the primary source of the reported phenomena. It is not clear whether the reported seismic activity is causally related to observed volcanic eruptions, or whether the volcanic activity is causally related to a major seismic event...We quote with explanations added by us in brackets where the text may be otherwise ambiguous "Late August, early September [1878] on various Aleutian Islands there occurred major volcanic eruptions accompanied by earthquakes. These include the islands of Amukt, Cheguk, and Umnak [Amukt may be Amukta, 250 km southwest of Okmok; Cheguk is unidentified, unless it is Chagulak Island NE of Amukta, towards the group of Islands of the Four Mountains]. The village of Makushin on Unalaska [Island] was destroyed by an earthquake" (Mushketov and Orlov, 1893).