|Enlarge ImageFigure 1. This plots shows drained lava lakes imaged using ABE equipped with a mechanically-scanned sonar [Cormier2003].
|Enlarge ImageFigure 2. This plot shows bathymetry of a rift valley at 17S on the Southern East Pacific Rise. This view shows the relationship between tectonic features and morphology such as volcanic domes [Cormier2003]. This data set has also be used to reconstruct the tectonic history of a rift valley [Carbotte2003].
|Enlarge ImageFigure 3. This map shows the bathymetry of the Lost City site. The detailed renderings of faults and the hydrothermal structures provide critical clues as to the mechanisms that control the hydrogeology at the newly discovered Lost City site [Kelley2005]
|Enlarge ImageFigure 4. These four panels summarize the plume data used to estimate vertical heat flux from the Endeavour Main Field in 2000. Starting on the upper left, the panels show vertical velocity, temperature, optical backscatter, and salinity
|Enlarge ImageFigure 5. This map shows the bathymetry of the Kilo Moana site in the Eastern Lau Basin.
|Enlarge ImageFigure 6. This photomosaic from the Kilo Moana site at the Eastern Lau basin was assembled automatically [Singh2004].
Precise navigation, robust control, and coregistered sensors
permit an AUV such as ABE to characterize the seafloor and the near-bottom
environment on the meter-scale through complementary sensing modalities.
Multibeam sonars on AUVs produce accurate bathymetric maps down to sub-meter
scales depending on the survey swath width and available navigation accuracy.
Magnetics data combined with the bathymetry shows crustal magnetization, which
permits the age and thickness of lava flows to be determined. Digital photos
provide details of lava flow types, sediment cover, and distribution of
animals. Water column data yields indications of plume activity and can be used
to estimate flow rates and fluxes of chemicals and heat from known sites and to
localize undiscovered hydrothermal sites.
Fine scale bathymetric and magnetic maps made using ABE have
provided geologists and geophysicists with new perspectives on important
seafloor processes. ABE maps have been used to identify volcanic features such
as lava flow units[Fornari2004], delimit their fronts, and estimate their
thickness either from magnetics data [Tivey1998] or from the depth of collapse
pits or the base level of lava tubes [Cormier2003]. An example is shown in Figure 1. Fine-scale bathymetry shows
tectonic features such as faults with great clarity, and resolves them into
multiple components [Tivey2003]. The meter-scale view also shows the
relationship between tectonic features and morphology such as volcanic domes [Cormier2003]
and hydrothermal vents [Fornari2004], an example is shown in Figure 2. ABE-derived bathymetry has also be used
to reconstruct the tectonic history of a rift valley by providing sufficient
detail and precision so that faults can be computationally removed to reveal
the dome-like structure from which the rift valley evolved [Carbotte2003]. In a
recent ABE cruise to the Atlantis Massif, detailed renderings of faults and the
hydrothermal structures provide critical clues as to the mechanisms that
control the hydrogeology at the newly discovered Lost
City site [Kelley2005], a map from that cruise is shown in Figure 3.
has also mapped and located hydrothermal plumes in new ways. ABE has
to measure the heat flux from a previously discovered hydrothermal vent
To estimate the heat flux, ABE carried instruments for temperature,
and three-axis water velocity while following a tight grid pattern
above the vent field [Yoerger2001a]. Mapping results showing vertical
velocity, temperature, salinity, and optical backscatter are shown in
In recent cruises to the Lau
176°12’W) [Langmuir2004] and the Southern Mid Atlantic Ridge (4°54’S, 12°28’W)
[German2005], we employed a
three-phase strategy [Langmuir2004, Jakuba2005] to locate and
hydrothermal vent sites. Starting with clues provided by towed systems
indicated a vent site within several kilometers, ABE executed a
grid patterns at increasing finer scales and increasingly close to the
seafloor. This sequence of dives located anomalies of temperature,
and electrochemical potential, permitting the vent site to be
pinpointed. ABE mapped the plume activity, built fine-scale
bathymetric maps of the vent fields and surrounding environment, and
photographed the vent structures and animal populations. An example of
fine-scale multibeam bathymetry from a vent site discovered on our Lau
cruise is shown in Figure 5.
To photograph the seafloor, ABE must maneuver within about 5
meters of the seafloor despite the presence of steep features several times
that height, such as those shown in Figure 5. Figure 6 shows a mosaic made
during the near-bottom or phase 3 survey that followed the phase 2 Lau
Basin dive shown in Figure 5. To
execute the survey, ABE had to manuever near the spires and cross over the
steep-walled grabens (depressions). The mosaic was made using a fully automated
technique [Singh] and allows vent animals to be identified and provides details
of the geology. Other uses for photographs taken by ABE have been to estimate
sediment thickness (hence age of the underlying lava) and to estimate effusion
rates of lava [Cormier2003].