The 2005 catastrophic acid crater lake drainage, lahar, and acidic aerosol formation at Mount Chiginagak volcano, Alaska, USA: Field observations and preliminary water and vegetation chemistry results

Abstract

[1] A mass of snow and ice 400-m-wide and 105-m-thick began melting in the summit crater of Mount Chiginagak volcano sometime between November 2004 and early May 2005, presumably owing to increased heat flux from the hydrothermal system, or possibly from magma intrusion and degassing. In early May 2005, an estimated 3.8 Â 10 6 m 3 of sulfurous, clay-rich debris and acidic water, with an accompanying acidic aerosol component, exited the crater through a tunnel at the base of a glacier that breaches the south crater rim. Over 27 km downstream, the acidic waters of the flood inundated an important salmon spawning drainage, acidifying Mother Goose Lake from surface to depth (approximately 0.5 km 3 in volume at a pH of 2.9 to 3.1), killing all aquatic life, and preventing the annual salmon run. Over 2 months later, crater lake water sampled 8 km downstream of the outlet after considerable dilution from glacial meltwater was a weak sulfuric acid solution (pH = 3.2, SO 4 = 504 mg/L, Cl = 53.6 mg/L, and F = 7.92 mg/L). The acid flood waters caused severe vegetation damage, including plant death and leaf kill along the flood path. The crater lake drainage was accompanied by an ambioructic flow of acidic aerosols that followed the flood path, contributing to defoliation and necrotic leaf damage to vegetation in a 29 km 2 area along and above affected streams, in areas to heights of over 150 m above stream level. Moss species killed in the event contained high levels of sulfur, indicating extremely elevated atmospheric sulfur content. The most abundant airborne phytotoxic constituent was likely sulfuric acid aerosols that were generated during the catastrophic partial crater lake drainage event. Two mechanisms of acidic aerosol formation are proposed: (1) generation of aerosol mist through turbulent flow of acidic water and (2) catastrophic gas exsolution. This previously undocumented phenomenon of simultaneous vegetationdamaging acidic aerosols accompanying drainage of an acidic crater lake has important implications for the study of hazards associated with active volcanic crater lakes.

Geomorphic consequences of volcanic eruptions in Alaska: A review

“…(Dorava and Meyer, 1994;Waythomas et al, 2013). Lahars at Alaska volcanoes may form by other mechanisms, such as drainage of crater lakes (Schaefer et al, 2008) or as a result of intense rainfall; however, these types of events occur rarely in comparison to lahars that form during eruptions.…”

Volcanic Lakes

“…A clear example of the formation of a volcanic lake after snowmelting is Chiginagak lake, Alaska (Fig. 6), where a lake was formed in 2005, followed by snow dam breakage and a lahar (Schaefer et al 2008). Many snow-capped volcanoes can potentially become the hosts of volcanic lakes after snow melting, when volcanic unrest resumes.…”

The Comparative Limnology of Lakes Nyos and Monoun, Cameroon

“…A confirmed gas release from a crater lake atop Mount Chiginagak volcano in 2005 differed in many respects from the Cameroonian disasters but showed some similarities. As elaborated by Schaefer et al (2008), this 105 m deep meltwater lake formed quickly in response to renewed upflow of heat and gas into a snow-and ice-filled crater. Water eventually burst through a cavity in the glacial ice impounding the upper *45 m of the lake and cascaded down the steep slopes into the valley below.…”

“…The Chiginagak region is remote and uninhabited, but vegetation bleached and killed by the acidic cloud preserved a record of its 29 km 2 area and height (Schaefer et al 2008), which indicate a volume comparable to the Lake Nyos gas cloud (*0.2-1 km 3 ). The huge size of the cloud suggests that the drop in lake level may have induced additional gas to exsolve from the lake water remaining in the crater or even vent rapidly from the underlying volcanic conduit.…”