Westdahl reported activity

Event Name : Westdahl 1820

Start:

1820

Observed

Tsunami:
Tephra plume:
Minor explosive eruption:

Eruption Type:	Explosive
MaxVEI:	2

Description: From Miller and others (1998): "Coats (1950) attributed four eruptions in the late eighteenth century and early nineteenth century to Pogromni volcano. Based on recent observations from aircraft, however, Pogromni does not appear to have been active in historical time. The eruptions should probably be assigned to Westdahl."

The eruption of 1820 is a little more confusing, as reports are unclear as to whether the event occurred on Unimak Island (containing the volcanoes of Westdahl, Pogromni, Fisher Caldera, Shishaldin, Isanotski, and Roundtop) or Umnak Island (containing the volcanoes Okmok, Recheshnoi, and Vsevidof). Modern compilers have attributed this event to Westdahl.

Soloviev and Go (1972) report: "1820, March 1 or the night of 2-3. A powerful volcanic eruption occurred on the northern tip of Umnak Island. The ashes spread as far as Unalaska and Unimak Islands. The eruption was accompanied by a strong earthquake. 'At dawn, it was observed that the sea had become more agitated' (Perrey, 1865 [in French])." Lander (1996) attributes this eruption to Pogromni, which is on southwest Unimak Island. Okmok Volcano is on the northeast of Umnak Island.

Lander (1996) writes "1820, March 1-2. Due to a strong eruption of Pogromni Volcano on the northern tip of Umnak Island [typographical error? Pogromni and Westdahl are on the southwestern side of Unimak Island], ashes injected into the air were observed as far away as Unalaska and Unimak [Another error? Westdahl and Pogromni are on Unimak] Islands. There was a strong earthquake on the night of March 1. The sea was observed to have became highly disturbed by dawn (Soloviev and Go, 1975: in Russian). Mushketov and Orlov (1893, p. 207-208: in Russian) describe the eruption has having taken place on February 19-20 (March 1-2 in Gregorian date) and another account dated March 1 referring to ash fall clouding the sea. Although the highly disturbed sea is suggestive of a tsunami, there is no specific mention of waves."

Mushketov and Orlov (1893, translated in 1994 by Katherine Arndt) wrote: "In 1820, on 19 February (Old Style) (in the night on the 20th), in a severe SE wind, on certain islands of the Aleutian Archipelago there were felt strong tremblings of the earth with a subterranean rumble. Immediately after, the air, it seemed, caught fire and clouds of ash and sand began to fall during the whole night. With the approach of day the wind changed, the volcanic matter stopped falling, but the sea was highly agitated. At the same time as these phenomena occurred on Unalaska, the volcano of Urimak [sic] Island, located 197 kilometers from Unalaska, began to produce eruptions which continued until August. (According to Postels, the active volcano was located on the north end of Umnak Island.) People who set out to look for the crater, due to the stinking steams tha thad spread for a verst, could not approach it and were convinced only that the island had increased in size and that the sea had rushed back for a considerable distance. Volcanic products erupted in such quantity that Urimak Island was covered with them for a radius of three miles around the crater. Postels describes these phenomena in the following manner: on 1 March on the north end of Umnak Island there occurred an eruption in which the ash reached Unalaska and Unimak. A strong earthquake, accompanied by a severe storm from the SE, plunged the inhabitants of Unalaska into terror. With the rising of the sun they saw that in certain places the earth was covered with ash more than a foot deep; the springs were choked with it, [and] the sea became cloudy, so that for a whole year fish were not seen in it and even whales appeared more rarely than usual. Not far from the site of eruption the Aleuts found amber in the loosened earth which covered the cliff that is washed by the lake." Mushketov and Orlov cite Malte Brun, Nouv. annales des voyages, XV, p. 131; Arago, Ann. de chimie et de phys., XXI, p. 396; and Postels, Voyage autour du monde, III, p. 24."

Coats (1950) reports a minor explosive eruption and Powers (1958) reports an ash eruption.