Distinctive Landforms Produced by Permafrost-Volcano Interactions, Arctic Alaska
[*James E. Beget*] (Alaska Volcano Observatory and Geophysical Institute,
University of Alaska, Fairbanks, AK. 99775-5780; ph: 01 907 474-5301; fax: 01
907 474-5163; email: ffjeb1@uaf.edu); Jeffrey Kargel (University of Arizona,
Tucson, Arizona, 85721); Rick Wessels (Alaska Volcano Observatory, U. S.
Geological Survey, Anchorage, AK. 99508), and Paul Layer (Geophysical Institute,
University of Alaska, Fairbanks, AK. 99775-5780)
Volcano-Permafrost interactions are responsible for several different kinds of
distinctive landforms at different sites in Arctic Alaska, where basaltic eruptions of
various ages and sizes have occurred in areas containing disseminated and massive
ground ice. On the Seward Peninsula at ca. 66° N, a series of giant composite
explosion craters as much as 10 km in diameter were produced by numerous
explosions where basaltic magma encountered water released by cryo-magmatic
interactions. The resultant Espenberg Maars are the largest known maar craters on
earth (Beget et al., 1996). New Ar/Ar dates indicate they formed at ca. 18kyr, 70
kyr, and 150 kyr., and so are correlative with times of cold climate and ground ice
more than ca. 100-m-thick ground ice during past full glacial periods (i.e. during
marine isotope stages 2, 4 and 6). The sedimentology of frozen ground and the
thermodynamics of magma-ground ice interactions can facilitate the generation of
repeated fuel-coolant explosions.
On the Seward Peninsula at Imuruk Lake at ca. 65° N the Lost Jim lava flow
advanced for more than 5 km over ice-rich permafrost and into the lake. The eruption
occurred only a few thousand years ago. The basaltic lava flow is bounded by steep
flow fronts and marginal levees as much as 20 m high. These flow margins terminate
in zones of complex thermokarst collapse features that record melting of ground ice
under the lava. These features indicate significant permafrost-magma interactions
occurred at the thin lava flow margins, and these interactions strongly influenced the
ability of the lava flows to travel across ice-rich areas,. The thermokarst features also
demonstrate that the lava flows were able to melt significant amounts of ground ice
even at thin lava flow margins several kilometers from the vent.
On the Yukon-Koyukuk Delta the Ingakslugwat Hills area at ca. 61.5° N. contains
several unusual composite volcanoes as much as 10 km long and 400 m high
composed largely of unconsolidated pyroclastic ejecta. Ingakslugwat, the Inupiaq
name for this site, can be translated as "mud hills", but coarser volcaniclastic material
is common around the vents. The volcanoes preserve numerous intersecting arms of
explosion craters of various ages that record multiple cycles of cryo-magmatic
explosive volcanism. Our currently preferred model for the origin of the
"Ingaksluwat" volcanoes involves cycles of eruptive activity occurring along linear
fissures interspersed with intervals of quiescence and ground ice formation.
ORAL
CORRESPONDING AUTHOR: JAMES BEGET