INVESTIGADORES
BELLOSI Eduardo Sergio
congresos y reuniones científicas
Título:
Fluvial response to an explosive eruption: the case of the Chaitén volcano and Blanco river (2008, Chile)
Autor/es:
UMAZANO, A.M., MELCHOR R., BEDATOU E., BELLOSI E., KRAUSE J.M.
Lugar:
Sao Paula
Reunión:
Congreso; 6th Latin American Congress of Sedimentology; 2013
Institución organizadora:
Latin American Congress of Sedimentology
Resumen:
The rhyolithic plinian eruption of the Chilean Chaiten volcano, initiated in May 2, 2008,
suddenly introduced abundant pyroclastic sediments in the Blanco river catchment area,
which experienced important modications. Before May 2, the river was characterized by
gravelly and low to moderate sinuosity channels crossing a low-gradient, vegetated and locally
urbanized (Chaiten city)
oodplain. This river, limited in the proximal part by steep and
densely forested highlands, was connected with the Pacic Ocean via a tidal
at. After heavy
rains in May 12-13, the river discharge increased due to breakout of logjams, which triggered
downstream responses including avulsion, changes in the pattern and dimensions of channels,
and construction of a delta. In this context, the goal of this contribution is to document
the sedimentological processes within a geomorphic framework. Downstream of the logjam
zone, deposits are composed by ash and lapilli, both pumice-rich and without important
participation of older sediments. The abandoned and lled paleochannel, and the proximal
part of splays experienced transient dilute
ows with variable sediment concentration and,
subordinately, hyperconcentrated
ows. The distal sectors of splays mostly record settling
from suspension. Upstream of the logjam zone, the deposits are composed of ash and lapilli
with paleovolcanic sediments, which record dilute
ows and the debris
ow-hyperconcentrated
ow continuum. We conclude that immediately after eruption, sedimentary dynamics of the
river was mainly controlled by a combination of high availability of incoherent pyroclastic
sediments on steep slopes, abundant rains, large logs that jammed the river and huge areas
of devasted forest.