JC24: Dating volcanoes on the Mid-Atlantic Ridge


Cruise diary

Tuesday 27 May 2008

Having spent Sunday and Monday collecting TOBI data from around the perimeter of the AVR, today was the first full day of the second phase of TOBI traverses. We are now in the process of making 21west to east traverses across the width of the AVR, which will allow us to not only build up a more detailed picture but also collect a variety of more detailed data, particularly magnetics, which will be useful for dating the lava flows, interpreting the AVR itself and possibly finding active hydrothermal vents. Chris Mallows and Tim have been busy stitching together the data from the past two days to produce a digital mosaic of the AVR and ‘draping’ it over the bathymetry so it can be viewed in 3D, making it easier to interpret.

A section of the  draped sidescan sonar digital mosaic of the AVR.
The lighter areas are areas of high backscatter and therefore the lowest
sediment cover and are probably the youngest lava flows.


Watches are continuing as normal. During the TOBI surveys the scientists are required to record and plot both the ship and TOBI’s position every half hour on a bathymetric map, an important job as it is then used to make sure TOBI’s flying high enough to avoid crashing into any obstacles, volcanic or otherwise. Time is also spent interpreting data, discussing where we would like to examine more closely with the ROV next week, and switching off each other’s music. 

Bram has been analysing the data from the first TOBI surveys and believes he may have located a plume in the water column on the eastern side of the AVR. He did this by looking at peaks in the degree of light scatter, which is an indication of how ‘dirty’ the water is. He then drew a fairly convincing graph of a stratified water plume, but we are yet to see whether it actually exists. Plumes are indicative of active hydrothermal vents and while finding hydrothermals are not one of this cruises major objectives, they are formed and sustained by heat from active volcanic processes. This is very relevant to this project as this shallow heat indicates this may be the location of recently active (and therefore the youngest on the AVR) volcanics and this has implications for the AVR’s development.

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May 2008