Hawaii's Kilauea Volcano, which until Tuesday had mainly been oozing lava through 20 fissures in the ground, is now sending ash clouds as high as 12,000 feet into the air.

The big picture: The volcano's latest eruption, which began on May 3, has moved into a new, more dangerous phase and shows no signs of stopping. The U.S. Geological Survey and National Oceanic and Atmospheric Administration have issued a "red" alert to ensure pilots avoid the ash cloud, which can damage modern jet engines.

The details: The more explosive eruptions and related ash clouds are happening because the lava lake level in the volcano's crater has drained all the way down to near the level of the water table. This is releasing a large amount of steam, and rocks that fall into the crater can block the steam from escaping into the air. This causes pressure to build up, resulting in more explosive eruptions.

In a May 16 eruption update, the U.S. Geological Survey (USGS) said they had discovered "dense ballistic blocks up to 60 cm (2 feet) across" in a parking lot a few hundred yards from the crater. "These reflect the most energetic explosions yet observed and could reflect the onset of steam-driven explosive activity," the agency said. "Further observations are necessary to asses this interpretation."

What's next: The USGS says more ash clouds, and potentially even more powerful eruptions, are possible with little advanced warning. Also, lava continues to flow and form new fissures. In other words, this isn't over.