The Puyehue-Cordon Caulle volcano in Chile spews ash during an eruption on June 14, 2011. The volcano spread ash through most of the Southern Hemisphere and disrupted hundreds of flights. File Photo courtesy of Chilean Air Force | License Photo
A volcanic eruption is one of the most powerful forces in nature, a seemingly unstoppable phenomenon that can have far-reaching impacts far beyond the area surrounding the volcano.
When a volcano erupts, many people think of lava spewing and oozing out of the ground and flowing through the nearby landscape, destroying everything in its path and reshaping the landscape forever. However, this is not the biggest danger brought on by a volcano.
"Volcanic-ash hazards are far-reaching and disruptive, affecting more people, infrastructure and daily activities than any other eruptive phenomena," the United States Geological Survey said.
Very fine grains of ash can be ejected tens of thousands of feet into the sky during a major eruption, but closer to the volcano, it can rain down like heavy snow that never melts.
The ash is typically made up of microscopic pieces of rock fragments, volcanic glass or a variety of minerals that do not dissolve in water.
"Falling ash can turn daylight into complete darkness," the USGS said. "Many people describe the experience as eerie and frightening, disorienting and confusing, or dreadful."
In extreme cases, this ash can pile up so much that it is measured in feet. In 1984, Rabaul, Papua New Guinea, was buried in volcanic ash that solidified cars in place and weighed down roofs to the point of collapse.
One particular danger posed by volcanic ash is that it can choke the engines of planes and commercial airliners flying anywhere in the vicinity. The fine, crushed rock can get into a plane's engine fan blades and choke off fuel.
A British Airways Boeing 747 twice had all four of its engines fail during a flight in 1982 when it flew near the Mount Galunggung volcano following an eruption. The crew ultimately restarted the engines and safely made an emergency landing in Indonesia.
The crew managed to safely navigate through the crisis, even though they had no idea what had caused the engines to fail. Pin pricks of light on the windscreen were the only indication that something was wrong, which turned out to be electrical sparks from the fine ash striking the windows at high speed.
Only a fraction of an inch of ash accumulation is needed to impact crops, livestock and infrastructure and require widespread clean-up. These issues can be compounded when it rains, particularly when ash falls on towns and cities as wet ash can conduct electricity, increasing the risk of a fire sparking.
Although it might look like ash from burned wood, volcanic ash is a very different substance.
"Though called ash, volcanic ash is not the product of combustion, like the soft fluffy material created by burning wood, leaves or paper. Volcanic ash is a hard rain of rough particles. It does not dissolve in water, is extremely abrasive and mildly corrosive and conducts electricity when wet," the USGS says.
Volcanic ash accumulates on buildings, and its weight can cause roofs to collapse. A dry layer of ash 4 inches thick weighs 120 to 200 pounds per square yard, and wet ash can weigh twice as much.
On top of the weight, ash can quickly clog ventilation systems and require people to frequently change the face mask that they are using to prevent inhaling the debris and to slow the spread of the coronavirus.
Depending on the wind, the ash can cause significant disruptions, not only in the areas immediately surrounding the volcano, but hundreds or even thousands of miles away.
Following the volcanic eruption on the Caribbean island of St. Vincent, winds blowing to the east sent clouds of ash over Barbados, located more than 100 miles east of the La Soufrière volcano.
People in Barbados were told to stay indoors due to the poor air quality with some residents describing the ash as "falling like snow." Wearing a mask when outside is also recommended, in addition to helping protect against COVID-19 infection.
Even when there is not a dense cloud of ash raining from the sky, the fine particles in the atmosphere can create chaos.
In 2010, air travel was shut down across much of Europe for a week after Eyjafjallajökull erupted in Iceland, sending a cloud of hazardous material over the continent.
Commercial airlines had to ground all of their planes that used jet engines as the very fine ash could get into the engines and cause them to stall, potentially causing the plane to crash, Science Magazine explained.
On a much larger scale, a significant, long-duration eruption could spew enough debris into the atmosphere to affect temperatures around the globe.
In the wake of a major volcanic eruption, the settled ash, along with other volcanic rock and rubble, can set the stage for a potentially disastrous weather-induced event known as a lahar.
Lahars are essentially large debris flows in which rock, mud and water tumble down a steep mountainside, sweeping away everything in their path.
"Volcanoes are a perfect setting for these events because of an abundance of steep, rocky rubble and a ready source of water in the form of rain, snow or ice," the USGS says.
About two years after Mount St. Helens cataclysmically erupted in 1980, a lahar was triggered near the mouth of the volcano that gushed downhill and eventually came to a stop 50 miles away, wiping out everything in its path.
Not all lahars are this big, and they can occur while a volcano is still erupting.
During the La Soufrière eruption on the island of St. Vincent, a dry river bed was filled with mud and debris from a lahar.
Folks that live in close proximity to a volcano should be prepared for both the long-lasting impacts of ashfall and the potential for lahars flowing off the steep terrain.
The USGS recommends people stay indoors to avoid exposure to ash, especially those with pre-existing respiratory conditions.
Experts advise that people who must travel outside amid the ash, even if it has settled on the ground and is no longer falling from the sky, should wear a face mask, pants, a long-sleeved shirt and goggles.