Reefer

It's amazing what can turn up even in well-visited areas. A 3D seabed mapping exercise has identified a new structure 130k off Cape York and Australia's Great Barrier Reef (https://www.theguardian.com/environment/2020/oct/28/scientists-discover-500-metre-tall-skyscraper-reef-at-australias-great-barrier-reef). This is a detached reef that is 1.5k at the base but then rises, to within 40m of the sea surface, in a thin shaft that is 500m tall. This makes it the same height as the Empire State Building in New York. The shaft must have existed, before being colonised by corals, as these organisms would not have been able to grow at the base.