threat at Makran is the build up of huge piles of submarine sediments. The Arabian oceanic plate is being subducted beneath the Eurasian continental plate, moving northward towards Iran and Pakistan. The sediment that has built up on top of the oceanic plate gets scraped off by the overlying plate and stuck onto the seafloor at the base of the coast.

Over geological time, this process has created one of the largest wedges of sediments on Earth, more than 7km thick in places. Earthquakes can make landslips in the wedge, causing the sediments to tumble down into the deeper ocean. But bizarrely, sometimes they can produce islands, too.

Tuesday’s earthquake shook those offshore sediments to the south of Pakistan. They are mainly muds and sands, rich in the rotted remainsof dead sea life that have fallen into the sediments over the millennia. Over time, this material has decomposed to gases like methane. When shaken up on Tuesday, these sediments seem to have erupted in a “mud volcano,” driven by the burping methane from the depths. An island of mud rose above the sea, emitting gas that could be set alight. In fact, locals who tried this had difficulty quenching the flame.

Mud volcanoes have been seen at the Makran subduction zone many times before. The 1945 earthquake triggered a number of mud volcanoes and offshore islands formed in the same region. More recently, one formed off Pakistan in November 2010. They all disappeared soon after, their soft material washed away by the ocean's waves and storms.

It is likely