Fossil and active fumaroles in the 1912 eruptive deposits, Valley of Ten Thousand Smokes, Alaska

Keith, Terry

Fumaroles in the ash-flow sheet emplaced during the 1912 eruption of Novarupta were intensely active throughout the Valley of Ten Thousand Smokes (VTTS) when first studied in 1917. Fumarole temperatures recorded in 1919 were as hot as 645°C. Influx of surface waters into the hot ash-flow sheet provided the fluid flow to sustain the fumaroles but also enhanced cooling so that by the mid-1930's vigorous activity survived only in the vent region. Configuration and distribution of high-temperature fissure fumaroles tens of meters long, that are prevalent in the middle and upper VTTS, were controlled largely by sintering and degree of welding, which in turn controlled fracturing and permeability of the ash-flow tuff. One fracture type developed parallel to the enclosing valley walls during compaction of the ash-flow sheet. Another type extends across the VTTS nearly perpendicular to the flow direction. A third type of randomly oriented fractures developed as cooling contraction cracks during vapor-phase devitirification. In distal parts of the ash-flow sheet where the tuff is nonwelded, prominent fumaroles have irregular funnel-shaped morphologies. Fumaroles distribution in the nonwelded part of the ash-flow sheet is concentrated above pre-emplacement river channels.

Fossil and active fumaroles in the 1912 eruptive deposits, Valley of Ten Thousand Smokes, Alaska

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