According to the article, people named this stuff "flammable ice" because______

Buried below the seabed around Japan, there are beds of methane, trapped in molecular cages of ice. In some places, the sediment covering these deposits of frozen water and methane has been eroded away, leaving whitish mounts of what looks like dirty ice rearing up out of the seafloor.
   Take a chunk of this stuff up to the surface and it looks and feels much like ice, except for a give-away fizzing sensation in the palm of your hand, but put a match to it and it doesn’t just melt, it ignites. Large international research programs and companies in Japan, among other countries, are racing to retrieve this strange, counter-intuitive substance — known as fiery ice — from beneath the seafloor to use its methane for fuel. If all goes to plan, they may even start extraction by the end of the next decade. But the journey so far has been far from smooth.
   There’s no doubt that methane hydrates could offer a major source of fuel, with recent estimates suggesting they constitute about a third of the total carbon held in other fossil fuels such as oil, gas and coal. Several nations, notably Japan, want to extract it. It is not hard to find, often leaving a characteristic seismic signature that can be detected by research vessels. The problem is retrieving that gas and bringing it to the surface.
   "One thing that’s clear is that we’re never going to go down and mine these icelike deposits, " says Carolyn Ruppel, who leads the US Geological Survey’s Gas Hydrates Project.
   It all comes down to physics. Methane hydrates are simply too sensitive to pressure and temperature to simply dig up and haul to land. They form at typically several hundred metres beneath the seafloor at water depths of about 500 metres, where pressures are much higher than at the surface, and temperatures are close to 0°C. Take them out of these conditions, and they begin to break down before the methane can be harnessed. But there are other ways to do it.