There's Something Wrong With One Of Hawaii's Volcanoes

Lava flowing off Hawaii's Big Island volcano into the sea. Juancat/Shutterstock

Thanks to its overly dramatic and rather persistent earthquake swarms, Yellowstone Caldera – America’s most infamous supervolcano – is getting all the attention lately, at least from the media. Volcanologists though are a little more concerned by what’s happening in Hawaii, and a new post by the United States Geological Survey (USGS) makes for some decidedly curious reading.

Technically speaking, Hawaii has been volcanically active since 1983, as lava has been continuously erupting from at least one vent – normally from Kilauea’s Puʻu ʻŌʻō vent – all this time. For the most part, those lava flows have fallen into the sea and haven’t bothered anyone at all. In fact, they’ve often put on quite the show.

However, along with the lava lake occasionally overflowing at Kilauea, volcanologists have noticed that the volcanic activity on Hawaii is higher than normal. In fact, back on September 17, 2015, the USGS raised the Volcano Alert Level – a form of geological caution labeling – from Green/Normal to Yellow/Advisory, meaning that people should be wary. Two years on, it’s still at that level.

Specifically, they are worried about Mauna Loa. This 700,000-year-old shield volcano is considered to be the largest single volcano (in terms of mass and volume) in the world and is one of the five major volcanoes that form the Island of Hawaii itself. Eruptions from this fiery mountain tend to be very fluid and non-explosive.

However, unlike plenty of volcanoes that erupt lava, Mauna Loa hasn’t done so since April 1984, which is an incredibly long time for an active volcano to remain quiet. Generally speaking, the longer a volcano remains silent for, the more explosive – or at least effusive – the next eruption will be.

A volcanologist watches a lava flow from Mauna Loa move towards him during the March-April 1984 eruption. P.W. Lipman/USGS

It’s Mauna Loa's dormancy that has led to it being labeled one of the world’s “Decade Volcanoes,” which are for various reasons the most dangerous on Earth. The USGS, as you would expect, is keeping an eye on it. It appears that the rates of ground inflation and seismic activity have remained unnervingly above background levels for several years now.

“In addition, we have detected more small magnitude (less than 3.0M) earthquakes beneath Mauna Loa than at any time since the previous eruption in 1984,” the USGS' post added. It’s these tremors that are worth keeping an eye on, as they are releasing about as much energy as they did prior to Mauna Loa’s last two major eruptions in 1975 and 1984.

However, the USGS cautions that although this is bizarre, there’s something missing from the volcano's shaky repertoire that means an eruption is likely not imminent. As the post explains, the USGS still hasn't detected any high-frequency quakes right at the summit of Mauna Loa yet – a sure sign that magma is about to breach the vent.

“But how certain is it that Mauna Loa will follow the script of 1975 and 1984?” it added. “That's the unknown.”

The USGS “cannot discount the possibility that Mauna Loa will move from current conditions to eruption more quickly than it did in 1975 and 1984,” but it also suggested that it’s possible that “the current unrest will gradually cease without the volcano erupting, as it did during periods of unrest in 2002 and 2004."

“And so, we must continue to live with uncertainty about the timing and details of Mauna Loa's next eruption.”

A Landsat mosaic of the Island of Hawaii. Mauna Loa is that dark green ridge with black lava flows adorning it. NOAA

In short, there simply isn’t enough historical data to make the call either way. An eruption at Mauna Loa, if particularly effusive, would potentially trigger local evacuations of those living in the lava's path. As such, the USGS suggests that residents should “be prepared” just in case.

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