Hull-mounted swath mapping systems and
towed vehicles have led to some remarkable
discoveries, particularly along the mid-ocean
ridge, the largest, most striking feature on the
planet at a length of 70,000 km throughout
all the world's ocean basins. This presentations
reviews the features and capabilities of the
hull-mounted Sea Beam 2000 swath mapping system,
as well as Argo II and DSL 120, towed vehicles of
the Woods Hole Deep Submergence Lab. Sea Beam 2000
provided the regional topography of a superfast spreading
center in the SE Pacific, but only the near-bottom
imaging capability of Argo II made it possible to obtain
the abundance and spatial distributions of fissures,
lava flows, and active hydrothermal vents. Argo II was
used in conjunction with DSL 120 to survey the narrow
axis of the southern East Pacific Rise at 17-18 S. The
DSL 120 was towed at ~75 m above the seafloor to collect
high resolution 120 kHz sidescan and bathymetry, while
Argo II was towed at ~ 8-9 m. Most data discussed come
from Argo II video, the Imagenex pencil-beam sonar mounted
on Argo II, and DSL 120 sonar. Processing of the image and
sonar data, in conjunction with novel GIS techniques will be
discussed. Preliminary results on show along-axis patterns of
fissures abundance cross-correlated with relative lava age
and hydrothermal vent abundance. In certain regions average
fissure widths and depths increase due to ridge crest
inflation and the propagation of intrusive dikes, resulting
from recent magmatic replenishment of an axial magma chamber
in the upper mantle, particularly at 17 25-28'S. To date, no
volcanic eruption on the ocean floor has been captured in real
time, but these results correlate well with the aftermath of
an eruptive event on the ridge discovered by a French submersible
team in 1993.
Keywords: seafloor survey technology, undersea imaging, GIS