Pahoa, Hawaii CNN  — 

A plume of ash from the Kilauea volcano rose 12,000 feet into the air before dropping ash on sections of the Big Island of Hawaii, prompting officials Tuesday to warn residents to stay indoors and airplanes to stay away from the area.

Since the Kilauea volcano erupted May 3, it’s been one nightmare after another for residents on the southeastern part of the Big Island.

The US Geological Survey issued a red alert Tuesday, which means a major eruption is imminent or underway and ash could affect air traffic

The USGS’ Michelle Coombs described the situation as ” very hazardous for aviation” and said her team isn’t quite sure what caused Tuesday’s slightly more intense ash emissions.

Norwegian Cruise Line announced that Pride of America would skip a call at Hilo on Tuesday and Kona on Wednesday. Instead, the ship will spend an extra day on the island of Maui.

People watch at a golf course as an ash plume rises from the Kilauea volcano on the Big Island.

US Geological Survey officials have said a phreatic eruption could happen at Halemaumau crater at the top of the Kilauea volcano. And it could send ash plumes as far as 12 miles from the summit crater, the Hawaiian Volcano Observatory said.

These are steam-driven explosions that occur when water beneath the ground or on the surface is heated by magma, lava, hot rocks or new volcanic deposits, the USGS says. The intense heat may cause that water to boil and result in eruptions.

Gas seeping out of cracks

Besides the ash, which is not poisonous, residents have to worry about choking on sulfur dioxide.

Coombs said the gas is coming out of 21 fissures, or cracks in the ground, caused by the volcano.

Levels of the toxic gas are dangerous in some places, Hawaii County officials said.

“Severe conditions may exist such as choking and inability to breathe,” the county’s civil defense agency said. “This is a serious situation that affects the entire exposed population.”

Officials warned residents to leave the area and get medical attention if they’re affected by the gas.

A fissure erupts from Kilauea near Pahoa, Hawaii. Chunks of rocks and magma fly with big explosions.

‘It sounded like hammers in the dryer’

Fissure 17 is the longest and has been shooting lava like a fountain and “sending spatter more than 100 feet into the air,” the Hawaiian Volcano Observatory said.

Coombs said the fissure had diminished in intensity, but officials said activity can go up just as quickly as it goes down.

Still, many of the fissures are emitting “quite a bit” of sulfur dioxide.

Two new fissures are small with not much lava coming from them, she said.

Ash plume is visible Tuesday near the Volcano Golf & Country Club, about 2 miles from Kilauea's crater.

CNN’s Stephanie Elam said her heart started pounding as she approached one fissure.

“It sounded like hammers in the dryer,” she said. “The molten rock was such a deep vibrant orange that it looked technically altered. When the sulfur dioxide hit my lungs once, it took my breath away.”

The Hawaii State Department of Health is asking the general public to avoid any area with fissures because the gases emitted require special cartridge respirators.

Toxic sulfur dioxide seeps out of the street in the community of Leilani Estates on the Big Island.

More eruptions could follow

Scorching lava has already swallowed dozens of homes and vehicles. So far, at least 37 structures have been destroyed, and counting.

In addition to the lava and toxic gases, now there are concerns about phreatic eruptions.

Those are steam-driven explosions that occur when water beneath the ground or on the surface is heated by magma, lava, hot rocks, or new volcanic deposits, the US Geological Survey says. The intense heat may cause that water to boil and result in eruptions.

But it will be difficult to warn residents who may be in the path of such an eruption.

Janet Babb, a geologist from the Hawaii volcano observatory, said phreatic eruptions are “notoriously hard to forecast, and can occur with little or no warning.”

CNN’s Scott McLean reported from Pahoa, while Steve Almasy and Faith Karimi wrote in Atlanta. CNN’s Chris Boyette, Joe Sutton and Keith Allen contributed to this report.