Surveying the Contours of an Underwater Mountain

Earth Observatory Blog

Surveying the Contours of an Underwater Mountain

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This week, the lab was buzzing with anticipation as we approached a seamount (an underwater mountain formed by volcanic activity), a small section of which had been mapped during last year’s MEGATERA cruise. The presence of the seamount was hardly a mystery, but details about its bathymetry were. We were about to get the first good look at this distinctive feature of the Wharton Basin. 

Since passing over the seamount four times in order to capture its contours as accurately as possible, MIRAGE scientists have learned that the seamount rises some 1,800 metres above the surrounding seafloor, is 30 or so kilometres across, and is cut from southeast to northwest by a deep fault. To the southeast of the seamount, one can detect a small basin, the result of a pull-apart fault, the same fault that appears to have cracked the seamount in two.

The seamount we surveyed this week is bisected by a deep fault running from the southeast (at the top of this image) to the northwest. Just above the seamount, in light blue (blue is the deepest and yellow is the shallowest), you can see evidence of a pull-apart basin created by the same fault running through the seamount.

Of keen interest to Dr Jerome Dyment is the age of the seamount, which he estimates could be anywhere from 50 to 64 million years old, depending on how it was formed. Another factor is the seamount’s composition—because it is composed of hard rock rather than soft sediments, as indicated by its bright reflectivity in echosounder imagery, it could be possible to identify markers on either side of the seamount’s fault, which could then help scientists determine how far along the fault line the two halves of the seamount have moved. And this information, assuming it can eventually be determined, could tell scientists more about the behaviour of faults in general throughout the Wharton Basin.

Beyond the excitement over the seamount’s geophysical and seismological characteristics, many of the students and scientists who have been patiently monitoring the bathymetry in the Marion Dufresne lab enjoyed seeing the seamount for a less scientific reason—they were simply happy to be looking at something other than relatively flat seafloor for a change!

To continue to follow the progress of MIRAGE, please check the EOS blog throughout the month of July, and spread the word using #MIRAGEcruise.

All photographs are taken by Ben Marks, unless otherwise stated.

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