Geomorphic processes influence human settlement on two islands in the Islands of Four Mountains, Alaska

Abstract

The Islands of Four Mountains island group of the Aleutian island arc is remote and difficult to access. Consequently, little fieldwork has focused on geomorphic processes and their relationship to island morphology, climatic change, and human settlement. We investigated glacial, fluvial, and slope processes on the morphologically different Carlisle, Cleveland, and Tana volcanoes. The islands were extensively glaciated at the last glacial maximum (LGM), and there is evidence for a Neoglacial advance. On the highly dissected Tana volcano, a large basin is likely the result of a pre-LGM sector collapse and subsequent glacial erosion into weak hydrothermally altered rock. Valley and moraine morphology is also influenced by hydrothermal alteration. On both Tana and Carlisle, there are sediment fans composed dominantly of thick debris flow deposits mantled by ~3 m of layered tephras, fine-grained alluvium, and anthropogenic deposits. Debris flow deposition was favored during the unstable paraglacial landscape of the early Holocene–latest Pleistocene. The earliest direct archaeological evidence for settlement is 3.8 cal ka BP, but soil geochemical evidence suggests that the islands were inhabited by 7.3 cal ka BP. This discrepancy in the archaeological record may be explained by geomorphic processes including coastal erosion and unstable geomorphic surfaces.

A 7300-yr-old environmental history of seabird, human, and volcano impacts on Carlisle Island (the Islands of Four Mountains, eastern Aleutians, Alaska)

“…So we suggest that the IFM were inhabited by 6900 cal yr BP, when the δ 15 N decline in the CR-03 peat deposit is observed. However, there are no other signs of human presence (archaeological or geomorphological) on the IFM at this time (Hatfield et al, 2019; Persico et al, 2018). The first archaeological traces of human occupation occur at about 4000 cal yr BP (Hatfield et al, 2019).…”

“…The first archaeological traces of human occupation occur at about 4000 cal yr BP (Hatfield et al, 2019). Perhaps the islands were inhabited earlier and that evidence has been buried or eroded (Persico et al, 2018). Further research at sites with older soil deposition may result in extended time depth for the human occupations in these islands (Hatfield et al, 2019).…”

“…In other cases, as at Kodiak Island, no increase in Ericales occurred after tephra deposition (Peteet and Mann, 1994). There is no evidence thus far of eruptions of Carlisle volcano in the Holocene (Persico et al, 2018) that could have directly influenced the Carlisle Island vegetation. The eruptions of other volcanoes (especially Cleveland volcano on the Chuginagak Island) were apparently not very destructive to vegetation; therefore, sharp changes in vegetation because of volcanism are not observed.…”

“…These meadows dominated by Cyperaceae are indicative of the cooler and wetter conditions of the Neoglacial (Heusser, 1973, 1983). The glacial advances associated with the Neoglacial event occurred in the Aleutians and western Alaska Peninsula after about 3000 yr BP (Thorson and Hamilton, 1986; Jordan and Krumhardt, 2003), and Persico et al (2018) note that a glacier was on Carlisle volcano during the Neoglacial.…”

“…Decreased precipitation and cooler conditions during the early Little Ice Age (LIA) attributable to a stronger Aleutian Low are described in numerous studies (Vaillencourt, 2013; Kaufman et al, 2016). Glacier readvance occurred on the Carlisle volcano during the LIA (Persico et al, 2018). There is decline of δ 13 C (Fig.…”