INTERACTIONS BETWEEN VOLCANISM, PERMAFROST, MILANKOVITCH CYCLES, AND CLIMATE CHANGE ON THE SEWARD PENINSULA

David Hopkins first recognized the importance of understanding volcanic processes when making interpretations of the Quaternary paleoecology of the Seward Peninsula of central Beringia. Large areas of the Seward Peninsula are buried by basaltic lava flows, but on the northern Seward Peninsula several enormous volcanic craters as much as 10 km in diameter, known as the Espenberg maars, formed by repeated explosive phreatomagmatic eruptions. These eruptions produced regionally extensive tephras, which are chemically similar to one-another and to non-explosive basalts exposed nearby. The basaltic maar craters are notable because they are significantly larger then maar craters found elsewhere on earth, and because the phreatic explosions which generated such huge maars resulted from magma-permafrost interactions. The youngest maar at Devil Mountain Lake has been radiocarbon-dated to ca. 18,000 14C ya. New Ar/Ar dates on pyroclastic ejecta from the older Killeak Lake Maars indicates they formed 61,000 ± 10,000 ya, while ejecta at the Whitefish Lake Maar was erupted ca. 160,000 ya. The geochronologic data suggests the Espenberg maars were influenced by Milankovitch cycles and climate change, as they formed during cold intervals corresponding to MIS 2, 4, and 6, when regional modelling linked to GCMs shows permafrost thicknesses were at a maximum across Beringia. In support of this hypothesis, we note that lava eruptions on the Seward Peninsula during the relatively mild Holocene have not generated explosive eruptions and large maars. Also, we report new Ar/Ar isochron dates on lava flows near the maars which fall near interglacial intervals corresponding to MIS 7 and 9. We propose huge maars are uncommon on the Seward Peninsula because they form only when eruptions occur at the culmination of major cold intervals, totalling perhaps only ca. 5-10% of the duration of the entire Quaternary.