More than 800 earthquakes have rattled Washington's Mount Rainier in the last 30 days, sparking fears that one of America's most dangerous volcanoes is coming to life.
More than half of the quakes, around 500, struck in July alone, with one intense swarm unleashing over 400 tremors in just 12 hours.
This towering stratovolcano looms over more than 3.3 million people across the Seattle-Tacoma metro area, threatening to cripple entire communities with ashfall, flooding, and catastrophic mudflows if it erupts.
Although Rainier has not produced a major eruption in over 1,000 years, earthquake swarms like this are often linked to volcanic unrest.
Such seismic activity is typically triggered by magma rising toward the surface, fracturing surrounding rock under intense pressure.
However, the US Geological Survey (USGS) has downplayed immediate eruption fears, saying the current tremors are likely caused by hot fluids, not magma.
Regardless, volcanologists have said that it is only a matter of time until Rainier, arguably the most dangerous volcano in the US, unleashes on the Pacific Northwest.
'Mount Rainier keeps me up at night because it poses such a great threat to the surrounding communities,' Jess Phoenix, a volcanologist and ambassador for the Union of Concerned Scientists told CNN.
When this volcano eventually blows, it won't be lava flows or choking clouds of ash that threaten surrounding cities, but the lahars: violent, fast-moving mudflows that can tear across entire communities in a matter of minutes.
Large lahars can crush, abrade, bury, or carry away almost anything in their paths, according to the USGS.
'Tacoma and South Seattle are built on 100-foot-thick ancient mudflows from eruptions of Mount Rainier,' Phoenix said.
But for now, the USGS has found 'no indication that the level of earthquake activity is cause for concern, and the alert level and color code for Mount Rainier remain at GREEN / NORMAL.'
The USGS issued a notice on July 9, informing the public that a major swarm had rattled Mount Rainier, which saw hundreds of earthquakes in half a day.
'Earthquakes are too small to be felt at the surface and will likely continue for several days. There would be no damage caused by such small events,' the USGS said.
Since the earthquake swarm, scientists have detected hundreds of more up to a 2.3 magnitude.
The USGS Cascades Volcano Observatory (CVO) added: 'Instruments do not show any detectable ground deformation at the volcano, and no anomalous signals have been seen on the infrasound monitoring stations.'
Volcanic eruptions usually cause lahars by rapidly melting snow and ice that covers the volcano's slopes, which then destabilizes loose dirt, rock and volcanic debris and causes it to flow rapidly downward.
But it doesn't always take an eruption to trigger a lahar, according to the Seismological Society of America.
Rarely, these powerful mudslides can form as the result of gradual weakening of the volcano's slopes due to past eruptions, or heavy rainfall after an eruption.
The deadliest lahar in recent history resulted from a 1985 eruption of the Nevado del Ruiz stratovolcano in Tolima, Columbia.
Within hours of the eruption, a torrent of mud, melted snow and rock inundated the town of Armero and killed an estimated 25,000 people.
This event, now known as the Armero tragedy, was the costliest volcanic disaster in history, according to The International Disaster Database. The total economic impact was estimated at $1 billion.
The 1980 eruption of Mount Saint Helens, located in Washington just 50 miles from Mount Rainier, also produced a dangerous lahar that destroyed more than 200 homes, over 185 miles of roads and contributed to the total death toll of 57 people.
These tragic events have helped scientists better understand the threat that lahars pose to human communities around active volcanoes, and experts are currently preparing for the terrifying possibility of a lahar forming at Mount Rainier.
