Geophysical observations demonstrate that the archipelagic apron surro
unding the Marquesan hot-spot volcanoes is derived almost entirely fro
m mass wasting processes. Seismic reflection and refraction data const
rain the volume of the apron sediments to approximately 200,000 km3, w
ith thicknesses reaching over 2 km in the deep portions of the moat ne
ar the edge of the volcanic edifice. Seismic velocities average 4 to 5
km s-1 in the sediments, and 6 km s-1 at the top of the underlying ba
sement. Single channel seismic profiles show acoustically chaotic core
s in the sediments of the apron, which are interpreted as debris flows
from mass wasting events. We deduce that the apron is formed by catas
trophic collapses that may involve volumes over 100 km3 tens to hundre
ds of times during the lifetime of a volcano. Comparison with similar
data from the Hawaiian Islands yields the result that the total volume
of volcanics and their derived sediments along the strike of the chai
ns is only slightly smaller for the Marquesas, implying comparable eru
ption rates. However, the ratio of sediment to surface volcanic load i
s much larger for the latter, leading to an overfilled moat in the Mar
quesas and an underfilled moat at Hawaii. The much larger size of the
Hawaiian islands can be explained as the combined effects of a higher
thermal swell, loading a stiffer elastic plate, and proportionately le
ss mass wasting.