A ship named Muirfield once struck an undersea mountain nobody had charted
More than 14,500 seamounts, drowned volcanoes rising at least a kilometre off the seafloor, stud the oceans, and most have never been studied closely. In 1973 one gave its name to the ship that hit it. Their bigger hazard is collapse: an ageing seamount's flank can slide away and trigger a massive tsunami.
Oceanographers define a seamount as an isolated, usually cone-shaped rise of 1,000 metres or more above the surrounding floor that stays below the surface. Most are extinct volcanoes, found near mid-ocean ridges, mantle plumes and island arcs, with summits hundreds to thousands of metres down in the deep sea. Beyond them lie more than 80,000 smaller knolls and hills. Some are still active, such as Kamaʻehuakanaloa, formerly Lōʻihi, off Hawaii.
They follow a life cycle of eruption, growth, subsidence and erosion. The largest may break the surface, where waves plane off the summit; after sinking again, these flat-topped peaks are called guyots or tablemounts. Mapped seamounts number 9,951, alongside 283 guyots. The North Pacific has the most, with seamounts and guyots covering 4.39 percent of its floor, and holds the three biggest guyots, led by Koko Guyot at an estimated 24,600 square kilometres. The Arctic has just 16 seamounts and no guyots. An average seamount spans about 790 square kilometres, and guyots average more than twice that.
Their height and the currents flowing around them draw in plankton, corals, fish and marine mammals, making seamounts among the most common marine ecosystems. Fishing fleets exploit that concentration, and stocks have crashed in documented cases such as the orange roughy. Bottom trawling, which scrapes entire communities off the slopes, causes about 95 percent of the ecological harm.
Charting remains incomplete, and bathymetric surveys and satellite altimetry are gradually filling the gaps. As seamounts age, material pushing into them builds pressure on their sides, and the resulting landslides are the greatest danger they pose, with the potential to unleash enormous waves.
Source: Seamount
