The United States Geological Survey’s (USGS) Hawaiian Volcano Observatory (HVO) has, in the past 24 hours, announced that that the volcano alert level at Kilauea has changed to “WARNING” and the aviation code to “RED” – so what exactly does this mean?

There’s been a lot of misinformation dropped online about this eruption. This has ranged from the curious (erroneous) connection between the perhaps poorly named “Ring of Fire” and Hawai’i – which is nowhere near said ring – to the entirely false idea that a south flank collapse at Kilauea could cause a Pacific-wide tsunami.

The phrase “red alert” is quite evocative and prime miscommunication fodder, so let’s break it down without any hyperbole. In general, this combined alert – which can be applied to a broad range of explosive and effusive eruption styles and volcanoes – means that a “major volcanic eruption is imminent, underway, or suspected with hazardous activity both on the ground and in the air.”

The reality isn’t quite so scary, though. The details behind the alert change can be found on the USGS update site itself: currently, ash emissions could increase or decrease in intensity depending on what’s going on within the conduit at Kilauea’s summit.

“At any time, activity may become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent,” the USGS explains. The phrase “more explosive” doesn’t mean anything particularly catastrophic, by the way – just more explosive, relative to its current state.

Dr Janine Krippner, a volcanologist at Concord University, told IFLScience that this alert “is an aviation warning because of the ash plume that was being produced yesterday. Ash is terrible for planes so USGS has put out this warning to communicate with them.”

A lot has happened since the eruption began a few weeks back; you can find a detailed account of the ongoing conflagration at the colossal shield volcano’s East Rift Zone (ERZ) here, courtesy of the USGS, and here, courtesy of volcanologist Erik Klemetti. In order to put this latest development into context, however, here are the relevant highlights.

An overflow of Kilauea’s summit lava lake at Halema’uma’u in late-April was followed a few days later by lava drainage-linked crater floor collapse at the volcanic cone Pu’u ‘O’o, an uptick in seismic activity, an ash-rich eruption at Pu’u ‘O’o, and the emergence of lava-effusing fissures in the nearby Leilani Estates.

At the same time, the lava lake at Halema’uma’u has drained to such an extent that there has been some concern that the eruption here could become far more explosive.

As the lava here has now fallen back into the conduit below the water level, steam is being generated. Right now, rock falls are creating pulses of vigorous ash emissions. If a rock fall blocks off the conduit, however, this could cause a huge steam-based pressure build-up, which could trigger a sizeable blast akin to the 1924 paroxysm.

The worry is that this could not only generate a prominent eruption column, whose ash threatens aviation and those on the ground, but it could further destabilize the structural integrity of the country rock here, causing further dangerous blockages.

As it happens, over the last few days, explosive activity at Halema’uma’u has intensified. As of Tuesday, May 15, ash from Halema’uma’u’s Overlook vent has risen to as high as 3,660 meters (around 12,000 feet). Volcanic air pollution, or “vog”, is drifting over nearby Pahala.

This ash generation is down to these rock falls and the explosive mingling of water and magma down in the conduit. Whether it be through a full blockage or just more rock falls and water-magma interactions, there’s a chance that the activity here will intensify somewhat.

That’s why the alert was issued – out of an abundance of conservative, well-reasoned caution, for those in the air and on the ground. Don’t believe the hype: as Krippner stressed (in all caps, originally), this will be “nothing like Mount St. Helens or Krakatau!”