There is a geological theory of Bryan Lovell explaining the strange underwater valleys at this spot halfway between Scotland and the Faroe Islands. Here you can find a network of river valleys beneath a km of water and a further 2 kilometres of sediment. The theory explaining this strange phenoma is hot blobs. A hot blob is a blob of hot mantle material rising up to the crust and pushing the crust up quickly (in geological terms). This piece of underwater area was pushed up and river valleys were eroded. Later on, it came down again and disappeared under water. It is still a theory, but Lovell is convinced he will be able to show his hot blob theory in many places on earth.
Source: NewScientist, 12 march 2011, p.41