The Largest Known Maars on Earth, Seward Peninsula, Northwest Alaska

The Espenberg Maars on the northern Seward Peninsula of Alaska were formed by a series of Pleistocene basaltic eruptions through thick permafrost. The maars were excavated as much as 300 m into older lithologies; ranging from 4 to 8 km in diameter, they are the four largest known maars on earth. Hydromagmatic eruptions which derive water from ground ice are evidently extremely explosive. The high heat capacity of ice in permafrost modulates the supply of water interacting with magma during the eruption, producing consistently low coolant-to-fuel ratios in an environment with a sustained, abundant water supply. The Espenberg Maars demonstrate that, under certain conditions, eruptions which involve the interaction of lava and permafrost are powerful enough to produce craters as large as small calderas.Les maars de l'Espenberg situés dans la partie septentrionale de la péninsule Seward en Alaska ont été formés par une série d'éruptions basaltiques datant du pléistocène, à travers une forte épaisseur de pergélisol. Les maars ont été creusés à une profondeur allant jusqu'à 300 m dans d'anciennes roches; d'un diamètre variant entre 4 et 8 km, ils sont les quatre plus grands maars connus sur Terre. Les éruptions hydromagmatiques qui tirent l'eau de la glace de sol sont, comme on l'a déjà constaté, extrêmement explosives. La grande capacité thermique de la glace dans le pergélisol détermine l'approvisionnement en eau qui interagit avec le magma au cours de l'éruption, donnant régulièrement lieu à un faible rapport refroidissant / combustible dans un environnement où l'eau est constamment abondante. Les maars de l'Espenberg démontrent que, dans certaines conditions, les éruptions qui déclenchent une interaction lave-pergélisol sont suffisamment puissantes pour donner naissance à des cratères de la grandeur de petites calderas

Vegetation and paleoclimate of the last interglacial period, central Alaska

The last interglacial period is thought to be the last time global climate was signi cantly warmer than present. New stratigraphic studies at Eva Creek, near Fairbanks, Alaska indicate a complex last interglacial record wherein periods of loess deposition alternated with periods of soil formation. The Eva Forest Bed appears to have formed about the time of or after deposition of the Old Crow tephra (dated to ~ 160 to ~ 120 ka), and is therefore correlated with the last interglacial period. Pollen, macrofossils, and soils from the Eva Forest Bed indicate that boreal forest was the dominant vegetation and precipitation may have been greater than present around Fairbanks during the peak of the last interglacial period. A new compilation of last interglacial localities indicates that boreal forest was extensive over interior Alaska and Yukon Territory. Boreal forest also extended beyond its present range onto the Seward and Baldwin Peninsulas, and probably migrated to higher elevations, now occupied by tundra, in the interior. Comparison of last interglacial pollen and macrofossil data with atmospheric general circulation model results shows both agreement and disagreement. Model results of warmer-than-present summers are in agreement with fossil data. However, numerous localities with boreal forest records are in conflict with model reconstructions of an extensive cool steppe in interior Alaska and much of Yukon Territory during the last interglacial

Stratigraphy and palaeoclimatic significance of Late Quaternary loess–palaeosol sequences of the Last Interglacial–Glacial cycle in central Alaska

Loess is one of the most widespread subaerialdeposits in Alaska and adjacent Yukon Territory and may have a history that goes back 3 Ma. Based on mineralogy and major and trace element chemistry, central Alaskan loess has a composition that is distinctive from other loess bodies of the world, although it is quartz-dominated. Central Alaskan loess was probably derived from a variety of rock types, including granites, metabasalts and schists. Detailed stratigraphic data and pedologic criteria indicate that, contrary to early studies, many palaeosols are present in central Alaskan loess sections. The buried soils indicate that loess sedimentation was episodic, or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input. As in China, loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess/soil formation cycle. Loess deposition in central Alaska took place before, and probably during the last interglacial period, during stadials of the mid-Wisconsin period, during the last glacial period and during the Holocene. An unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period. Our studies lead us to conclude that vegetation plays a key role in loess accumulation in Alaska. Factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods. The most important of these is vegetation; boreal forest serves as an effective loess trap, but sparsely distributed herb tundra does not. Thus, thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central Alaska. Much of the stratigraphic diversity of North American loess, including that found in the Central Lowlands, the Great Plains, and Alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors