Surveying with multibeam echo-sounders around old (>>1 Ma) volcanic ocean
islands reveals that their submarine flanks contain a strong downslope-oriented ridge-and-
valley corrugation, which modifies the original volcanic morphology of lava terraces
and cones. By analogy with canyons in other settings, this corrugation was probably
caused by channel incision by erosive sedimentary mass flows such as turbidity currents
and debris flows. We adapt a method first used in subaerial geomorphology to isolate th
e
erosion depth (exhumation) and apply it to the eroded flanks of the 6-8 Ma Anaga massif
of Tenerife. The channels formed around this massif divert around local topographic
highs. These highs, which are probably original volcanic cones, are therefore
preferentially preserved during erosion, so that their elevations can be used to construct
an artificial reference surface. Terrain depth was calculated by subtracting this refer
ence
surface from measured bathymetry. Comparison of the terrain depth of the old, eroded
submarine flank of Anaga with that of the young, mostly unaltered submarine flank of El
Hierro allows us to infer the mean depth of Anaga's submarine erosion, which is ~100 m.
Volcanic terrains can be dated by radiometric methods, so they also provide a way of
quantifying long-term denudation rates. We infer that submarine denudation of Anaga
has occurred at comparable rates to that of subaerial lowlands and much slower than
denudation of highlands, illustrated locally by the more extensive erosion of the subaerial
Anaga edifice.
N. C. Mitchell, W. B. Dade and D. G. Masson
Erosion of the submarine flanks of the Canary Islands, J. Geophys. Res.-Earth Surface, 2003 (DOI: 10.1029/2002JF000003).