A massive underwater volcano erupted in the island nation of Tonga this past weekend, triggering shockwaves that were experienced around the world, including in the Chicago area.
Tsunami warnings were initially issued, but the threat began to recede Sunday - one day after the Hunga Ha’apai volcano sent large waves crashing ashore and people rushing to higher ground.
Measurable shockwaves generated from the violent eruption were reported across the globe and even felt away as far away as Mount Hood in Oregon, according to the United States Geological Survey.
In the Chicago area, the eruption caused pressure fluctuations that were recorded at multiple weather stations, including at O'Hare International Airport, according to the National Weather Service office in Romeoville.
A portion of the shockwave, the eastward-propagating part, reached the Chicago area between roughly 8:20 and 8:30 a.m. Saturday, with a clear spike in pressure observed around that time, according to NWS.
But that wasn't the only occurrence.
After traveling across Asia, Africa and Europe, the westward-propagating part of the shockwave reached the Chicago area early Sunday morning. It then caused an additional jump in pressure readings shortly after midnight, the NWS tweeted.
Large booms were heard as far as Alaska as the eruption led to a tsunami across portions of coastal Alaska, according to the NWS.
Tsunamis also caused damage to boats as far away as New Zealand and Santa Cruz, California, but did not appear to result in any widespread damage.
The USGS estimated the eruption caused the equivalent of a magnitude 5.8 earthquake. Scientists said tsunamis generated by volcanoes rather than earthquakes are relatively rare.
The Hunga Tonga Hunga Ha’apai volcano is located about 64 kilometers north of Nuku’alofa. In late 2014 and early 2015, a series of eruptions in the area created a small new island and disrupted international air travel to the Pacific archipelago for several days.
There is not a significant difference between volcanoes underwater and on land, and underwater volcanoes become bigger as they erupt, at some point usually breaching the surface, said Hans Schwaiger, a research geophysicist with the Alaska Volcano Observatory.
With underwater volcanoes, however, the water can add to the explosivity of the eruption as it hits the lava, Schwaiger added.
Before an explosion, there is generally an increase in small local earthquakes at the volcano, but depending on how far it is from land, that may not be felt by residents along the shoreline, Schwaiger said.