One of the largest landslides in history didn't occur on land, but underwater, just off the coast of Norway. It also didn't occur in recent history, but in the Holocene epoch, about 8,000 years ago. Known as the Storegga Submarine Landslide, the event caused massive amounts of sediments to slide about 497 miles (800 kilometers) down the continental slope. This in turn triggered a mega-tsunami, perhaps 82 feet (25 meters) high, that struck Norway and Scotland.
In 1998, Russian researchers discovered an unstable hydrate field near the site of the Storegga slide. Now scientists believe that a rapid decomposition of hydrates, related to temperature and pressure changes coming at the end of the last ice age, destabilized the sediments and caused the landslide.
The Risky Business of Mining Methane Hydrate
The potential rewards of releasing methane from gas hydrate fields must be balanced with the risks. And the risks are significant. Let's start first with challenges facing mining companies and their workers. Most methane hydrate deposits are located in seafloor sediments. That means drilling rigs must be able to reach down through more than 1,600 feet (500 meters) of water and then, because hydrates are generally located far underground, another several thousand feet before they can begin extraction. Hydrates also tend to form along the lower margins of continental slopes, where the seabed falls away from the relatively shallow shelf toward the abyss. The roughly sloping seafloor makes it difficult to run pipeline.
Even if you can situate a rig safely, methane hydrate is unstable once it's removed from the high pressures and low temperatures of the deep sea. Methane begins to escape even as it's being transported to the surface. Unless there's a way to prevent this leakage of natural gas, extraction won't be efficient. It will be a bit like hauling up well water using a pail riddled with holes.
Believe it or not, this leakage may be the least of the worries. Many geologists suspect that gas hydrates play an important role in stabilizing the seafloor. Drilling in these oceanic deposits could destabilize the seabed, causing vast swaths of sediment to slide for miles down the continental slope. Evidence suggests that such underwater landslides have occurred in the past (see sidebar), with devastating consequences. The movement of so much sediment would certainly trigger massive tsunamis similar to those seen in the Indian Ocean tsunami of December 2004.
But perhaps the biggest concern is how methane hydrate mining could affect global warming. Scientists already know that hydrate deposits naturally release small amounts of methane. The gas works itself skyward -- either bubbling up through permafrost or ocean water -- until it's released into the atmosphere. Once methane is in the atmosphere, it becomes a greenhouse gas even more efficient than carbon dioxide at trapping solar radiation. Some experts fear that drilling in hydrate deposits could cause catastrophic releases of methane that would greatly accelerate global warming.
Does that make methane from hydrate fields off-limits? This is the question scientists from all over the world are trying to answer.