Abstract
The 2008-2009 eruption of Chaiten Volcano (Chile) involved a variety of volcanic and associated hydro- logic processes that damaged nearby forests. These processes included coarse (gravel) and fine (silt to sand) tephra fall, a laterally directed blast, fluvial deposition of remobilized tephra, a variety of low-temperature mass-movement processes, and a pyroclastic flow. Each of these geophysical processes constitutes a type of ecosystem disturbance which involves a distinctive suite of disturbance mechanisms, namely burial by tephra and sediment, heating, abrasion, impact force, and canopy loading (accumulation of tephra in tree crowns). Each process affected specific areas, and created patches and disturbance gradients in the forest landscape. Coarse tephra ('gravel rain', >5 cm depth) abraded foliage from tree canopies over an area of approximately 50 km 2 north-northeast of the vent. Fine tephra (>10 cm depth) accumulated in tree crowns and led to breakage of branches in old forest and bowing of flexible, young trees over an area of about 480 km 2 . A directed blast down the north flank of the volcano damaged forest over an area of 4 km 2 . This blast zone included an area of tree removal near the crater rim, toppled forest farther down the slope, and standing, scorched forest around the blast perimeter. Fluvial deposition of >100 cm of remobilized tephra, beginning about 10 days after initiation of the erup- tion, buried floodplain forest in distinct, elongate streamside patches covering 5 km 2 of the lower 19 km of the Rayas River and several km 2 of the lower Chaiten River. Across this array of disturbance processes the fate of affected trees varied from complete mortality in the tree removal and pyroclastic flow areas, to no mortality in areas of thin tephra fall deposits. Tree damage included defoliation, loss of branches, snapping of tree trunks, abrasion of bark and ephiphytes, and uprooting. Damaged trees sprouted from epicormic buds located in trunks and branches, but sprouting varied over time among disturbance mechanisms and species. Although some effects of the Chaiten eruption are very similar to those from the 1980 eruption of Mount St. Helens (USA), interactions between biota and geophysical processes at Chaiten produced some unique effects. Examination of vegetation response helps interpret geophysical processes, and disturbance mechanisms influence early stages of biotic response to an eruption.
Highlights
Explosive volcanism involves a variety of volcanic and associated hydrological processes with many environmental effects (Ayris and Delmelle, 2012)
This paper focuses on geology and ecology perspectives of the 2008-2009 eruption of Chaitén
We conducted field sampling in austral summers of 2009 through 2013 to characterize vegetation damage in terms relevant to interpreting disturbance mechanisms of burial, heat, abrasion, impact force, and canopy loading across the areas affected by the principal volcanic and hydrologic processes (Fig. 1, Table 1)
Summary
Explosive volcanism involves a variety of volcanic and associated hydrological processes with many environmental effects (Ayris and Delmelle, 2012) When such eruptions occur, a synthesis of geology, ecology, and geography perspectives helps reveal the nature of volcanic and hydrologic processes, their effects on vegetation, and the patterning of those effects on the landscape (e.g., Dale et al, 2005). Primary disturbances may lead to secondary disturbances (e.g., fluvial redeposition of tephra, debris slides resulting from loss of root strength of killed trees). Both primary and secondary disturbances produce distinct geographic features, termed landscape patches or disturbance zones
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