Nc. Mitchell et al., Seafloor slopes at mid-ocean ridges from submersible observations and implications for interpreting geology from seafloor topography, EARTH PLAN, 183(3-4), 2000, pp. 543-555
Observations from 145 submersible dives are used to create a database of mi
d-ocean ridge scarp topography and lithology. Seafloor lithologies are clas
sified into extrusives, basaltic talus, dykes, gabbros and serpentinites, a
nd the dive locations are broadly classified according to whether they are
close to transform valleys and as a function of ridge spreading rate. The d
atabase is used to determine whether there is any difference in the maximum
slope for each rock type, which might relate to differences in rock jointi
ng, cohesion or friction properties. There is a common perception that lowe
r crustal rocks form steeper slopes than shallower crustal rocks but until
now there has been little evidence to support or refute this idea. From our
analysis we find a tendency for gabbro and dykes to form steeper slopes th
an serpentinite. The 90th percentile of each lithology slope distribution,
used as a measure of limiting slope, is 43 degrees, 39 degrees and 32 degre
es for gabbro, dykes and serpentinite, respectively. Lithologic control on
slope is weak, however, compared to overall slope variability in these mid-
ocean ridge settings so seafloor relief is likely to be a poor guide to und
erlying geology. We speculate on the structure of eroding fault scarps, out
line the implications for attempts to infer active faults from talus ramp a
ctivity and discuss more generally factors affecting the geomorphology of m
id-ocean ridge slopes. (C) 2000 Elsevier Science B.V. All rights reserved.