National Geographic: If efforts fail to cap the leaking Deepwater Horizon wellhead in the Gulf of Mexico (map), oil could gush for years–poisoning coastal habitats for decades, experts say. Last week the joint federal-industry task force charged with managing the spill tried unsuccessfully to lower a 93-ton containment dome (pictures) over one of three ruptures in the rig’s downed pipe. Crystals of methane hydrates in the freezing depths clogged an opening on the box, preventing it from funneling …