The height of a guyot as measured from the surrounding regional sea floor t
o the volcano's slope break records the water depth at the time the guyot s
ubmerged. Thus guyot heights maybe used as indicators of the paleodepth of
the surrounding ocean floor. We compile data on the heights of 68 intraplat
e guyots and atolls in the Pacific Ocean as well as 46 volcanic islands in
the:Pacific, Atlantic, and Indian Oceans. We find that guyot heights genera
lly increase with the age of the lithosphere upon which they were emplaced,
although there is a large amount of scatter. In nearly all cases, seamount
height, and thus seafloor paleodepth,:is less than expected of normal seaf
loor. These results suggest that most of the volcanoes in this study formed
on anomalously shallow seafloor, consistent with formation at hotspots. To
characterize thermal anomalies associated with these hotspot swells, we mo
del guyot heights by calculating the isostatic uplift predicted for normal
lithosphere that has been partly reheated and is underlain by anomalously h
ot mantle. This model is able to explain the anomalous water depth at most
of the seamounts with hotspot thermal anomalies of 100 degrees-300 degrees
C, The heights of a few volcanic chains, however, are not anomalously low,
suggesting that these volcanoes are not associated-with hotspots. In additi
on, the observed trend of Hawaiian-Emperor guyot heights as well as the sub
dued morphology and gravity signature of the oldest Emperor seamounts suppo
rts our hypothesis that Cretaceous age Meiji seamount may have formed on or
near a spreading center.