Debris Flows Associated With Lava Extrusion at Three Stratocones; Cleveland, Pavlof (Alaska) and Stromboli (Italy)

Debris flows that occur contemporaneously with lava flow extrusion have been observed visually, with handheld thermal infrared cameras and in Advanced Very High Resolution Radiometer (AVHRR) satellite data at Stromboli, Cleveland and Pavlof. At Pavlof these debris flows can also be identified in the seismic record. These basaltic equivalents of block and ash flows are low energy, low velocity, low temperature (200- 300° C) with varying grain sizes. Deposits of these flows show little or no sorting. They originate from the 'A'a× flow front but form a cohesive flow with minor elutriation of ash. Further downslope they precede and underly lava flows, partly guiding the path of later flows. At Pavlof and Cleveland they lie on top of layers of snow and ice. At Pavlof this has resulted in these flows feeding lahars, at Cleveland they form an insulating layer between the snow and the active lava flow. Field evidence has shown that the snow layer can even be present years after the emplacement of the lava flow on top of the debris flow. This suggests that this layering is an integral part of the structure of the volcanic cone, providing preferred failure planes and resulting in instability. In the future this could result in either failure of large parts of the volcanic edifice of these volcanoes or large scale phreato-magmatic explosions. The handheld thermal imagery of these debris flows obtained on Stromboli will provide a clearer insight into their thermal regime, and when combined with satellite and seismic data, a hazard assessment of these flows can be made.