HAVE EXPLOSIVE VOLCANIC ERUPTIONS AFFECTED THE HUMAN COLONIZATION OF THE ALEUTIAN ARCHIPELAGO? A WORK IN PROGRESS

Although reoccupation of landscapes by humans after volcanic crises is clearly demonstrated in continental settings, the influence of volcanic devastation on human habitation of volcanic archipelagos is a complex problem. During the Holocene, two episodes of migration and colonization by humans of distinct cultures established the Unangan/Aleut peoples of the Aleutian Islands. Interestingly, these people persisted at the same time the geologic record shows that explosive and effusive volcanic activity was particularly high. The small land area of the islands, the nature of marine subsistence in a sub-Arctic environment, and the presence of volcanic calderas, created by devastating eruptions, highlight the importance of establishing the timing of large eruptions relative to the timing of occupation revealed in the archeological record. By examining the existing record of radiocarbon dated tephras, this study sought to determine whether there were spatial or temporal patterns in the explosive eruptive activity. From ~158 to 178° W longitude, 55 distinct tephras represent significant explosive eruptions of the last 12,000 years. Initial results suggest that the Andreanof and Fox Islands of the archipelago have had frequent explosive eruptions. However, one clear result of the investigation is that sampling bias strongly influences the apparent patterns. The sampling bias incorporates at least three confounding variables to consider during statistical analysis: larger island size allows more opportunity for geologic preservation of tephras; larger magnitude eruption promotes tephra preservation by creating thicker and more widespread deposits; the characterization of tephras for each island varies widely because of logistical and financial limitations. This preliminary investigation proposes variables to mitigate sampling bias and recommends sampling strategies to facilitate statistically valid examination of research questions. Initial indications are that a period of relative quiescence existed from 4,800 to 6,000 yBP. Also, though caldera-forming eruptions occurred throughout the Holocene – and several remain undated – four occurred across the archipelago between 8,000-9,100 yBP (during the Early Anangula Phase). Finally, no Holocene tephras have been found in the Near Islands.