People worried Mount Rainier may be erupting; it was just a cloud

The United States Geological Survey said Wednesday that fears of an imminent Mount Rainier eruption were unsubstantiated. Reports on social media said steam was “venting” from the volcano, but the USGS said it was actually a cloud and not the result of any geologic activity.

Concerns that Mount Rainier was awakening first materialized Wednesday afternoon when a meteorologist at KOMO, Seattle’s ABC affiliate, tweeted a video that appeared to show steam venting from the volcanic mountain’s crater. The clip quickly went viral, amassing 812,000 views by Thursday morning.

The USGS quickly dismissed rumors of an eruption but did not comment on whether the volcano was venting – or exhaling pent-up gases and/or lava and pyroclastic materials such as ash.

“The sort of behavior seen in this video is not unusual,” the agency wrote at 10:09 a.m. .

In a subsequent news release, however, it confirmed that a “new vent has NOT opened on the volcano.”

“After looking at the data we collect, the USGS seismic network does not show any unusual levels of activity coming from Mount Rainier,” the agency wrote.

So if Wednesday’s apparition was not a spurt of steam and was nonvolcanic in origin, what was it?

A cloud. Just a cloud.

A number of webcams operated by the National Park Service and located closer to the crater captured the innocuous cloud forming as moisture-rich air was forced up the summit. As the air ascended, it cooled to its dew point, meaning the parcels reached saturation and the contained moisture condensed. That formed a cloud that poured over the lip of the ridge, appearing similar to steam emanating from the crater.

Weather balloon data from the mouth of the Quillayute River, about 75 miles west of Seattle, showed a very narrow level of moisture present at 14,150 feet. That is probably the layer that rode up and over the edge of the volcano, where it was cooled to saturation.

The air above and below was drier, meaning there were not any other clouds to obscure the view.

Mount Rainier is about 60 miles from downtown Seattle and rises to 14,411 feet in elevation. An active stratovolcano, it is the highest mountain in Washington state and a staple of the Cascades. The last minor eruption occurred in the early-to-mid-1800s, but eyewitnesses reported other eruptive activity during the latter half of the 19th century.

Despite its rather somnolent appearance since, it was named by the International Association of Volcanology and Chemistry of the Earth’s Interior as one of the 16 most potentially dangerous volcanoes in the world, given its proximity to Seattle.

It has been roughly 1,000 years since the last magmatic eruption at Mount Rainier, but that did not stop Twitter from quickly devolving into a snowballing of speculation – and perhaps a bit of snark. Some users fearfully asked follow-up questions, while others dared the universe to throw another wild card into the mix.

“Sure, why not add an active volcano incident to the bingo card at this point?” tweeted one user.

“Let’s hear what (the volcano) has to say,” wrote another.

Others went on to make humorous quips likening the volcano to the Roman Catholic Church’s tradition of using white smoke to announce the naming of a new pope – instead jeering that the volcano is an auger portending success by the Seattle Mariners.

“It’s white smoke, the Mariners playoff drought is over,” wrote @MarinersMuse on Twitter.

One woman even joked about turning the debacle into a drinking game, tweeting: “Me sitting here wondering how many times @USGSVolcanoes has to say this is a cloud formation. And should I make it a drinking game while reading these tweets.”

The agency went on to discourage heavy alcohol use, writing back: “We would not recommend (a drinking game). Alcohol poisoning would definitely be a possibility.”

The USGS news release said the cloud seen was a lenticular cloud, which forms “when moist air is pushed up and over the top of a mountain, forming a disc shape.” Lenticulars commonly form over Mount Rainier.

However, Wednesday’s cloud atop the summit was rough, asymmetric and not nearly as stratified as a classic lenticular, which often resembles a flying saucer.