japanmeltdownA state of emergency has been declared at six nuclear reactors in Japan — one of which is in the midst of a partial meltdown — following last week’s tsunami, according to the Associated Press. More than 170,000 people were evacuated over fears of the radioactive contamination that would follow a full meltdown at those locations.

Radiation levels briefly tipped past legal limits in the area around the Fukushima Dai-ichi power plant following an explosion in one of the reactor cores. Workers are now racing to cool the core’s fuel rods and prevent a possible second explosion at another of the facility’s reactor units.

The tsunami was caused by a 9.0 earthquake that occurred on Friday off the eastern coast of Japan, one strong enough to shift the Earth’s axis by 6.5 inches, The Los Angeles Times reports. The Fukushima Dai-Chi plant’s Unit 1 experienced a hydrogen blast on Saturday in the wake of the natural disaster, after an attempt to relieve pressure in the core’s containment chamber resulted in an explosion. Officials are now using sea water mixed with boron, which disrupts nuclear chain reactions, to cool the overheating cores.

The lack of power is the key crisis being faced as efforts are underway to prevent a widespread nuclear disaster from occurring, physicist Ken Bergeron explained in a Saturday media briefing (via Scientific American).

“To keep that decay heat of the uranium from melting the core, you have to keep water on it. And the conventional sources of water, the electricity that provides the power for pumps, have failed. So they are using some very unusual methods of getting water into the core, they’re using steam-driven turbines—they’re operating off of the steam generated by the reactor itself.”

He further notes that this will all unfold “in a matter of days,” and that restoring power is “crucial” to bringing the plants back under control.