Gravity Anomalies in the Galapagos Islands Area

Watts, A. B.; Cochran, James R.; Case, J. E.; Ryland, S. L.; Simkin, Tom; Howard, K. A.

In a recent report Case et al. (1)
presented a free-air gravity anomaly
map of the Galapagos Islands based on
32 gravity stations on the islands. On
the basis of their data they stated that
the Galapagos Islands are associated
with an east-west trending "residual
negative anomaly" which is superimposed
on a "broader positive anomaly
of unknown amplitude and extent."
They concluded that "the gravity data
can be most readily interpreted in terms
of a low-density fegion related to a hot
spot or plume" beneath the islands.
We believe, however, that the data
of Case et al. in no way support this
interpretation. Their observations can,
in fact, be explained simply if the
Galapagos Islands are in some form of
isostatic equilibrium. Any form of isostatic
compensation will result in an
"edge effect" in the free-air anomaly
at the location of a large change in
relief. For a relatively narrow feature,
the edge effect anomalies over the two
"edges" merge, resulting in a large
positive anomaly. For a wider feature,
the two edge effects become separated,
resulting in an area of less positive
anomalies over the center of the feature.



Also Published In


More About This Work

Academic Units
Lamont-Doherty Earth Observatory
Marine Geology and Geophysics
American Association for the Advancement of Science
Published Here
January 13, 2015