Erosional characteristics and behaviour of large pyroclastic density currents
Geology, v.40, n.11, pp. 1035-1038 doi:10.1130/G33380.1
Factors influencing the erosive behavior of large pyroclastic density currents (PDCs), both mainly massive and thinly stratified, are not well understood. To investigate the parameters influencing the erosive behavior of PDCs produced during the flowing phase of large, caldera-forming Plinian (Campanian Ignimbrite) and phreatoplinian (Neapolitan Yellow Tuff) eruptions, we use scoured fall deposits at the base of, or interstratified with, PDC deposits from the Campanian region of Italy. At several localities, we calculated the depth of PDC erosion by comparing the measured thickness of eroded remnants to reconstructed thickness at each site (estimated by isopach mapping), and recorded the (1) distance from vent, (2) elevation of the locality, and (3) paleoslopes. Furthermore, we have considered how these factors can be influenced by outcrop exposure. Depth of erosion correlates with distance from the vent in low-relief landscape, while across very rugged topography the only related parameter is elevation. The different erosive patterns appear to show how pyroclastic currents interact with the topography in the surrounding terrain. When a PDC crosses relatively flat surfaces, it decelerates away from the vent, decreasing its erosive capacity; but when moving through steep terrain, a PDC accelerates down the valley, increasing its erosive capacity.