All around the world we have stored methane in places like the permafrost of the Russian North and in clathrates beneath the sea. Most are stored and not released mainly due to the temperatures that those areas currently have, but the climate is changing and places like Russia may release large quantities of it from the frozen vegetation and through mining. Most coal mine release some methane, but some of those in Russia release disproportionally more than other areas, some mines releasing the same amounts all whole other states or countries outside.
Methane is a powerful global warming gas being around 80 times that of CO2 and methane levels have been rising faster than CO2 levels. The lowest sea floor is pretty stable as far as temperatures go, so there seems little effect from surface warming, but the likelihood is that as the earth is very hot underneath where ‘hot spots’ move around, they may at some time hit a major methane/clathrate pocket as they go. Places like Hawaii are on a long line of visible and hidden volcanoes where those weaker spots in the earth have moved in a particular line Hawaii being just one point on this.
We know very little of the clathrate density and size beneath the oceans, so we can’t be sure whether a large pocket of clathrates suddenly heating up and causing a methane burst will be in a direct line and predictable at some time.
One thing is sure, the world would be totally unprepared for it and the effects in the short term and especially long term.
There is some circumstantial evidence this has already happened in the past many times.