Minerals Report - International Seabed Authority

some of these seamounts are the size of continental mountain ranges, some
are elongated ridges, some are quite large and some of them have flat tops.
When studying crusts deposits on seamounts, in particular with the
objective of finding extensive, thick and high-grade deposits, the first step
according to Dr. Hein is to map the seamounts using multi-beam echo
sounder and side-scan sonar systems. The typical methodology has been to
produce Sea Beam bathymetric maps, derivative backscatter maps, and slopeangle
maps. Simultaneously, using single or multi-channel seismic systems,
Dr. Hein pointed out that seismic profiles are taken to, inter alia, look at the
structure of the seamount with depth.
With a cross-section of a seamount, Dr. Hein illustrated slopes of
seamounts of about 14 degrees. He also showed areas on the seamount where
there is slumping, where the slope of the seamount has undergone mass
movement and there is slumping on the slope. He pointed out that the crusts
are going to be thinner in those areas where there has been re-working on the
slopes of seamounts. He also pointed out that mass wasting is a major
problem for the evolution of thick crusts. He informed participants that there
is such a tremendous amount of motion of materials down the flanks of
seamounts that they constantly destroy crusts. The crusts then have to start
growing again. On this subject, Dr. Hein informed participants that there
have been very good studies done on the Hawaiian chain on mass wasting.
He also informed participants that as part of its research efforts, USGS
undertook studies to construct a map on a group of seamounts in the Marshall
Islands EEZ to determine the distribution of mass wasting deposits, areas
containing sediments and areas containing hard rocks.
Dr. Hein said that seamounts obstruct the flow of oceanic water
masses, thereby creating a wide-array of seamount generated currents of
generally enhanced energy relative to flow away from the seamount. The
effects of these currents are strongest at the outer rim of the summit region of
the seamount, the area where the thickest crusts are found. Dr. Hein also said
that the seamount-generated currents could be traced for at least several
hundred metres above their summits. Other water column features produced
by the interaction of seamounts and currents are density inversions, isotherm
displacements, enhanced turbulent mixing and up welling. According to Dr.
Hein, the up welling process moves cold, nutrient-rich waters to shallower
INTERNATIONAL SEABED AUTHORITY 261