Probability of landslide is acceptable why because the area is tectonically very active. But these crescent depressions are on plane area rather than on any slopy area. thats the twist. 

Mark Keiter, i am attaching both Multibeam as well as subbottom image of the same area.

Drishya, do u have any ROV picture....

Sachin

thank you for putting the images..  i dont have the ROV pic.

Was the seabed in this area formerly glaciated?

this area is far away from land/continental shelf area. This all crescent depressions are occuring at a water depth of 700m. 

Thanks. From the images they looked like they could be of glacial origin.

Mark 

how much the possibility of glacial scars in an area 700m water depth ??

Iceberg scour has been found in water depths of up to 500m offshore Ireland

http://www.journalofmaps.com/crossrefMap.php?mid=1092 

But in this area chance of occurrence of glacier is meager. This area is nearer to a major rift basin.

thank you for the paper Mark. 

Hi Drishya,

I would suggest possible landslides and Mass Transport Deposits (MTDs) directed towards the south? MTDs will generate crescentic scarps and depressions in the extensional upslope (headwall) region that in some instances cut down into more lithified sediments. Such instabilities can develop on very gentle slopes (less than 1 degree) and in some instances less than 0.25 degrees, so the fact that your features are on a 'plane' may not be such an issue. They are obviously more prone to develop in tectonically active areas, and are frequently of the scale you describe. I attach a couple of links to references on instabilities and MTDs  in 'negligible slopes' that may be of interest.

Thanks

Ian

Article Fold and fabric relationships in temporally and spatially ev...

Article Seismogenic slump folds formed by gravity-driven tectonics d...

It must be tension in two directions to make the arc. The seafloor is moving, but not uniformly.

Hi

 Thank you for the valid suggestion Alsop and Issigonis

Alsop unfortunately i could not able to download the paper you suggested.If you wont mind can you send through my mail. My mail id is [email protected]/ [email protected]

That will be a great help. 

Michael Sir, could you please elaborate it, how tension is creating in two direction and what could be the other possibility for the development of such arc shaped structure when sea bottom is hard.

As it is well known that Indian plate is moving in the north and north east direction and a clock wise rotation is also involve. Simultaneously central Andaman rift zone is also providing compressional stress.

Here what could be the possibility of rock type. Whether such crescent shape structure   may develop in the flow basalt, at junction of the two units. Because at this particular point sediment get no time to establish and getting removed by the contour current. Is it write?

Presumably thin crust near seamount, so suggest detailed gravity traverse to investigate isostatic equilibrium. It has been suggested that oceanic island basalts are a recent addition to the mantle.possibly the result of partial melting of material that has arisen from a separately convecting lower mantle. The crescents could result from interaction of this rising material with thin(

Have you considered fluid flow features e.g., pockmarks? For instance, crescent pockmarks ca. 1500 wide and ca. 150 deep have been documented in the South China Sea (cf. Morphologies, classification and genesis of pockmarks, mud volcanoes and associated fluid escape features in the northern Zhongjiannan Basin, South China Sea). Best wishes!

Dear Omosanya 

The chance of pockmarks we checked with subbottom profiler. But there is no such indications Most of the pock marks are rounded no?! the crescent one ...thats a new thing for me ...will try to find out more...

Dear Mcclure,

Gravity traverse we made it. But the data we have to check it thoroughly. These seamounts are of ~cretaceous age . Thank you for your suggestion. will try to crack geophysical data.

Crescent shaped pockmarks can easily occur due to remodelling of seafloor depressions by the activity of currents following their initial formation. This may lead to the depressions being partially infilled by sediment. Crescent shaped depressions of up to 12 km in diameter have been found on the Chatham Rise (New Zealand) (http://www.tandfonline.com/doi/abs/10.1080/00288306.2011.589860 and http://oceanrep.geomar.de/21515/1/geomar_rep7.pdf). I cannot see from the sub-bottom profiles that you uploaded whether this is a possibility here. Another possible explanation could be related to current scour and contourite style deposits associated with current flow around the seamounts? 

Hi,

thank you for the papers.its quiet interesting.still doubt...

contourite deposits and scour can easily form in a  sediments. Whether it will act same as in hard rock??

I doubt this would be the case, I wasn't sure from your original post whether there was sediment cover on the seafloor and just the base of the depressions was hard bottom, or whether the whole area is hard bottom? 

Jess, I think you are on to something. Could it be that it is lack of sedimentation, like when you get snow drift you get snow everywhere EXCEPT in a crescent around an obstacle?

 Sachin Kumar Tripathi  

I am interested in the interaction between isostasy and geomorphology, not specifically OIB or oceanic geophysics, but there are some relevant references in CRM Fowler's 'The Solid Earth' Cambridge 1990 pp254-255 and 335-337. Hope this helps.

Dear Hillman i am again attaching some new image of the sub bottom profiler...

Ulf - yes I think this could be the case, if there is sedimentation in the region that has been scoured by currents flowing around the seamounts, you might expect to see 'drifts', as you get in snow. This is similar to what was found on the Chatham Rise, there are significant 'scours' around the base of submarine volcanic seamounts - as shown in the Collins paper linked above. 

Sachin - I am afraid I cannot see much detail in the images you have posted here. Can you identify any features such as sediment drifts in the sub-bottom profile data? Do the scours / depressions truncate strata? 

Hillman,at many places sediment drift is very much visible, but at this particular point mainly at crescent part it seems to be non depositional area. What could you identified from above image? Just elaborate it.

i am attaching another image.

Thanks

Hillman, it also very difficult to calculate the rock density  from sub bottom reflectors.