|One of the evacuation signs that have appeared recently around NYC.|
The methane hydrate deposits along the east coast may be giving way, melting, like those in the Arctic are. If so, and if the wind blows the resulting gas plumes west instead of east, then there will be potentially gigantic methane clouds coming ashore, causing raging fires and explosions as they sweep inland from the coasts, igniting whenever the gas meets a flame and is concentrated enough.
How powerful might such explosions be? Well, this news story talks about a study recently commissioned by the federal government to determine how badly a 10-kiloton nuclear blast would damage Washington D.C. That means they probably envision that as being the upper range of the force generated by a large methane plume exploding over/on one of our major cities.