Overview of ABE's mapping capabilities

Print version E-mail to a friend
Text Size: Change text to small (default) Change text to medium Change text to large
null
Enlarge Image
Figure 1. This plots shows drained lava lakes imaged using ABE equipped with a mechanically-scanned sonar [Cormier2003].


null
Enlarge Image
Figure 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].


null
Enlarge Image
Figure 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]


null
Enlarge Image
Figure 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


null
Enlarge Image
Figure 5. This map shows the bathymetry of the Kilo Moana site in the Eastern Lau Basin.


null
Enlarge Image
Figure 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.

ABE has also mapped and located hydrothermal plumes in new ways. ABE has been used to measure the heat flux from a previously discovered hydrothermal vent field [Stahr2000]. To estimate the heat flux, ABE carried instruments for temperature, salinity, and three-axis water velocity while following a tight grid pattern repeatedly above the vent field [Yoerger2001a]. Mapping results showing vertical velocity, temperature, salinity, and optical backscatter are shown in figure 4.

In recent cruises to the Lau Basin (20°9’S, 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 characterize undiscovered hydrothermal vent sites. Starting with clues provided by towed systems that indicated a vent site within several kilometers, ABE executed a sequence of grid patterns at increasing finer scales and increasingly close to the seafloor. This sequence of dives located anomalies of temperature, optical backscatter, 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 finally photographed the vent structures and animal populations. An example of fine-scale multibeam bathymetry from a vent site discovered on our Lau Basin 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].



 

WHOI logo

Last updated February 16, 2007
© Woods Hole Oceanographic Institution. All rights reserved