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Snowy reported activity




Event Name : Snowy 2000

Start: 2000 Observed

Fumarolic or hydrothermal activity: BibCard
Steam: BibCard
Eruption Type:Not an eruption.

Description: From Neal and others (2004): "In mid-September 2000, AVO received a pilot report of a steam plume emanating from a depression in the surface of the upper Aguchik Glacier about 3 mi (5 km) SE of the summit peaks of Snowy Mountain * * * According to the pilot, Kodiak Air Service owner Willy Hall, this was the first time in his many years flying the region that he had seen either the depression or the accompanying steam. Hall also reported a strong sulfur smell while in the vicinity.

"At AVO's request, NPS Unit Manager and pilot John Bundy photographed the area from the air on September 29 and again on October 8 [see fig. 4 in original text]. The anomalous depression is roughly circular in shape, several hundred meters in diameter, and marked by concentric, nested crevasses that enclose a steep-walled opening of unknown depth. The crevassed ice defining the depression slopes towards the hole with increasing severity until nearly vertical ice-walls define the opening, also roughly circular in shape. Based on crude estimates of crevasse scale, we estimate the opening to be about 15-30 m (60-100 ft) across. This feature occurs on a portion of the icefield that flows generally to the southeast with a slope of about 8°; meltwater from this glacier eventually

drains into Kukak Bay. Geographic coordinates first reported by Willy Hall are 58°17.69' N, 154°38.78' W, placing the hole at an elevation of about 975 m (3,200 ft).

"In Bundy's photos from both September 29 and October 8, a faint wisp of steam emerging from the orifice is visible. High winds and turbulence quickly dissipated the steam during the Bundy flights, but the original pilot report estimated the steam plume to rise 100-200 ft (30-60 m). Neither Bundy nor Hall observed other fumaroles in the area, including the nearby summit peaks of Snowy Mountain. Actively steaming fumaroles had been recorded at the highest Snowy peak in 1982 (Kienle and Swanson, 1983; Motyka and others, 1993), however, over the past several summers, USGS geologists Judy Fierstein and Wes Hildreth noted no sulfur smell or trace of fumarolic activity anywhere on the Snowy edifice.

" * * * Based on several lines of evidence, the depression, central orifice, and minor, transient steam plume appear to be new features. We are not able to locate a similar structure on air photos from 1984 nor on Landsat images from 6 September 1999. It is uncertain exactly when the feature developed or became visible, however, based on Hall's comments, it was likely sometime during

summer 2000. The gradual 'sag' towards the central orifice indicated by crevassing patterns suggests the depression developed slowly (perhaps over years?) rather than suddenly during a rapid deformation or melting event that would have produced steep ice walls (John Paskievitch, pers. comm. 2000). On the other hand, the feature is quite similar in appearance to the 'subsidence

bowl' that developed over eruptive vents at Vatnajokull, Iceland, in 1996.

"AVO detected no significant change in background seismicity in the area over the course of the year, arguing against an intrusive event or significant acceleration of hydrothermal activity. However, the southeast Snowy edifice is not well-captured within the Katmai area seismic net and very small events may have gone undetected (John Power, pers. comm. 2003). It is possible that

changes in the surface of the glacier - retreat or other mass balance changes - have allowed an older feature to become more prominent at the surface."

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Page modified: March 30, 2017 14:36
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