TSUNAMIGENIC
EFFICIENCY OF VOLCANICALLY, SEISMICALLY AND GRAVITATIONALLY INDUCED
ISLAND EDIFICE MASS FAILURES AND OF AERIAL AND SUBMARINE LANDSLIDES
George
Pararas-Carayannis
Abstract
of poster presentation prepared for the 32nd International Geological
Congress, (T11.15 (115) Tsunami hazard from slope instability),
Florence, Italy, August 20-28, 2004
ABSTRACT
 Short
and longer period impulsive waves can be generated in the open
ocean - or in confined bodies of water - by a variety of volcanic
island edifice mass failures and by volcanically, seismically
or gravitationally induced aerial or submarine landslides and rock
falls.
Regardless
of the nature of the triggering event, the kinematic processes
of  volcanic mass edifice failures
and of submarine landslides are complex phenomena and result
in different types of impact interaction with the water mass.
The
resulting mechanisms of wave generation and their tsunamigenic
efficiency depend on the nature, speed and energy of the triggering
source event. Additional factors are the volume and physical
dimensions of the water displacing mass, the type of slide, the
spatial coherency or deformation of the slide flow or rotation,
the elongational and shear strain of the slide, the frictional
effects of adjacent geologic formations, the hydrodynamic impact
on initial and subsequent water crater formations and water surface
deformations, as well as the resulting water vorticity, turbulence,
geometrical spreading, divergence and wave height attenuation.
Flank
instability of Kilauea volcano on the island of Hawaii. Hawaii's southern slope
showing coastal faults parallel to the east rift zone of the
Kilauea volcano, and the Hilina Slump along which slope failures
have been occurring (Modified after Morgan et al. 2001).
Impulsively generated waves from such complex source mechanisms
can be expected to behave non-linearly and to change significantly
away from the sourceregion, with varying near and far field effects
and terminal run up heights.
Evaluation
of such processes for several historic events, leads to the conclusion
that volcanic edifice mass failures, impact rock falls and submarine
landslides have the potential of generating destructive local
waves in confined bodies of water and in the near field environment
of an open ocean coast. However the heights of these waves attenuate
rapidly with distance because of relatively smaller source dimensions
and shorter wave periods.
Specifically
evaluated for their tsunamigenic efficiency are the mechanisms
of past massive submarine landslides and of flank failures of
island stratovolcanoes in the Hawaiian Islands, in the Caribbean
and Mediterranean Seas, and in the Atlantic and Indian Oceans.
Flank
instability of Cumbre Vieja volcano on the island of La Palma.
Relief Map of
the island of La Palma in the Canary Islands showing the volcanoes
of Taburiente, Cumbre Nueva Cumbre Vieja and the north-south
trending rift zone and secondary faults.
Flank
instability of the Piton De La Fournaise volcano on Reunion Island
Reunion Island
in the Indian Ocean and the Piton De La Fournaise volcano showing
extensive erosion, subsidence and an arcuate coastline suggestive
of underwater slope failure.(Source: GEOSAT photos)
Map of the
Island of Vulcano in Italy where a 200,000 cubic meter massive
flank failure on the northeast side generated local tsunami
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