Did you hear that? No? Did you hear anything? No? If you’re currently standing on or near a volcano, you have thirty minutes or less to run like heck because it’s about to blow. That’s the conclusion of scientists studying a volcano in Nicaragua. They found that some volcanoes have a half-hour ‘lull before the storm’ – or in this case, eruption – that is a warning it’s about to spew.
Carnegie Mellon volcanologist Diana Roman led a team that monitored the Telica Volcano in Nicaragua from 2009 to 2011 when it had a month-long series of eruptions. Telica is a stratovolcano, 1061 meters (3,500 feet) high with six cones and a double crater. It has a history of frequent eruptions dating back to a major one in 1529. The team had the volcano covered with monitoring gear to within 4 km (2.5 miles) of the summit and were ready for the 2011 activity.
What they weren’t ready for were the eerie silences prior to the eruptions. According to their study published in Earth and Planetary Science Letters, a total of 50 explosions were recorded. Of those, 35 were preceded by a period of quiet for at least 30 minutes in duration, 13 were silent for less than 30 minutes and only two never had a lull.
The volcanologists then compared the length of the calm periods to the amount of energy released by the subsequent eruptions and found a direct correlation. The longest time of silence (10.3 hours) preceded the greatest explosion.
The study notes that these were sulfur dioxide gas eruptions, not magma, and that provides the explanation for the calm before the volcanic storm. The eruptions appear to have been caused by gas vents being sealed, resulting in a quiet buildup of pressure until a gas-and-ash explosion. The vents seem to have been plugged up by mineral-laden water seeping into cracks and hardening or by rocks filling the holes, possibly moved by previous eruptions … a never-ending cycle of plug-calm-explode-plug-calm-explode again.
According to Roman, this is the first real-time monitoring of this phenomenon and the indications are that the quieting is disquieting.
Similar observations of this phenomenon have been noted anecdotally elsewhere. Our work has now quantified that quiet periods can be used for eruption forecasts and that longer quiet periods at recently active volcanoes could indicate a higher risk of energetic eruptions.
On your vacation to Yellowstone this summer, you may want to put down your phone, speak in whispers and keep your ear to the ground.