David Kitchen, University of Richmond Volcanoes inspire awe with spectacular eruptions and incandescent rivers of lava, but often their deadliest hazard is what quietly falls from the sky. When a large volcano erupts, as Mount Spurr appears close to doing about 80 miles from Anchorage, Alaska, it can release enormous volumes of ash. Fine ash can infiltrate the lungs of people and animals who breathe it in, poison crops and disrupt aquatic life. Thick deposits of ash can collapse roofs, cripple utilities and disrupt transport networks. Ash may lack the visual impact of flowing lava, but as a geologist who studies disasters, I’m aware that ash travels farther, lasts longer and leaves deep scars.

Volcanic ash: What it is, and why it matters

Volcanic ash forms when viscous magma – molten rock from deep beneath Earth’s surface – erupts, exploding into shards of rock, mineral and glass carried in a near-supersonic stream of hot gas. Towering clouds of ash rise several miles into the atmosphere, where the ash is captured by high-altitude winds that can carry it hundreds or even thousands of miles. As the volcanic ash settles back to Earth, it accumulates in layers that typically decrease in thickness with distance from the eruption source. Near the vent, the ash may be several feet deep, but communities farther away may see only a dusting.

Breathing danger: Health risks from ash

Breathing volcanic ash can irritate the throat and lungs, trigger asthma attacks and aggravate chronic respiratory conditions such as COPD. The finest particles pose the greatest risk because they can penetrate deep into the lungs and cause death by asphyxiation in the worst cases. Mild, short-term symptoms often resolve with rest. However, the long-term consequences of ash exposure can include silicosis, a lung disease and a possible cause of cancer. The danger increases in dry regions where fallen ash can be kicked up into the air again by wind or human activity.

Risks to pets and livestock

Humans aren’t the only ones at risk. Animals experience similar respiratory symptoms to humans. Domestic pets can develop respiratory distress, eye inflammation and paw irritation from exposure to ash.

Livestock face greater dangers. If grazing animals eat volcanic ash, it can damage their teeth, block their intestines and poison them. During the 2010 Eyjafjallajökull eruption in Iceland, farmers were advised to shelter sheep and cattle because the ash contained fluoride concentrations above the recognized safety threshold of 400 parts per million. Animals that remained exposed became sick and some died.

Harm to crops, soil and water

Soil and crops can also be damaged. Volcanic ash alters the acidity of soil and introduces harmful elements such as arsenic and sulfur into the environment. While the ash can add nutrients such as potassium and phosphorus that enhance fertility, the immediate impact is mostly harmful. Ash can smother crops, block sunlight and clog the tiny stomata, or pores, in leaves that allow plants to exchange gases with the atmosphere. It can also introduce toxins that render food unmarketable. Vegetables, fruit trees and vines are particularly vulnerable, but even sturdy cereals and grasses can die if ash remains on leaves or poisons emerging shoots. Following the 1991 Mount Pinatubo eruption, vast tracts of farmland in central Luzon in the Philippines were rendered unproductive for years due to acidic ash and buried topsoil. If multiple ashfalls occur in a growing season, crop failure becomes a near certainty. It was the cause of a historic famine that followed the eruption of Mount Tambora in 1815.

Ash can also contaminate surface water by introducing toxins and increasing the water’s acidity. The toxins can leach into groundwater, contaminating wells. Fine ash particles can also settle in waterways and smother aquatic plants and animals. During the 2008 Chaitén eruption in Chile, ash contamination led to widespread fish deaths in the Río Blanco.

Ash can ground airplanes, gum up infrastructure

Ash clouds are extremely dangerous to aircraft. The glassy ash particles melt when sucked into jet turbines, clog fuel systems and can stall engines in midair. In 1982, British Airways Flight 9 lost power in all four engines after flying through an ash cloud. A similar incident occurred in 1989 to KLM Flight 867 over Alaska. In 2010, Iceland’s Eyjafjallajökull eruption grounded more than 100,000 flights across Europe, disrupting travel for over 10 million passengers and costing the global economy billions of dollars. Volcanic ash can also wreak havoc on infrastructure by clogging water supplies, short-circuiting electrical systems and collapsing roofs under its weight. It can disrupt transportation, communication, rescue and power networks, as the 1991 eruption of Mount Pinatubo in the Philippines dramatically demonstrated.

What to do during ashfall

During an ashfall event, the most effective strategy to stay safe is to stay indoors as much as possible and avoid inhaling ash particles. Anyone who must go outside should wear a properly fitted N95 or P2 mask. Cloth masks provide little protection against fine ash. Rainwater tanks, troughs and open wells should be covered and monitored for contamination. Livestock should be moved to clean pastures or given uncontaminated fodder.

To reduce structural damage, ash should be cleared from roofs and gutters promptly, especially before rainfall. Older adults, children and people who are sick are at greatest risk, particularly those living in poorly ventilated homes. Rural communities that are dependent on agriculture and livestock are disproportionately affected by ashfall, as are low-income people who lack access to clean water, protective masks or safe shelter. Communities can stay informed about ash risks through official alerts, including those from the Volcanic Ash Advisory Centers, which monitor ash dispersion and issue timely warnings. The International Volcanic Health Hazard Network also offers guidelines on personal protection, emergency planning and ash cleanup.

The long tail of ash

Volcanic ash may fall quietly, but its effects are widespread, persistent and potentially deadly. It poses a chronic threat to health, agriculture, infrastructure and aquatic systems. Recognizing the risk is a crucial first step to protecting lives. Effective planning and public awareness can further help reduce the damage. David Kitchen, Associate Professor of Geology, University of Richmond This article is republished from The Conversation under a Creative Commons license. Read the original article.

Richard E. Peltier, UMass Amherst The Trump administration is “reconsidering” more than 30 air pollution regulations, and it offered industries a brief window to apply for exemptions that would allow them to stop following many air quality regulations immediately if approved. All of the exemptions involve rules finalized in 2024 and include regulations for hazardous air pollutants that cause asthma, heart disease and cancer. The results – if regulations are ultimately rolled back and if those rollbacks and any exemptions stand up to court challenges – could impact air quality across the United States. “Reconsideration” is a term used to review or modify a government regulation. While Environmental Protection Agency Administrator Lee Zeldin provided few details, the breadth of the regulations being reconsidered affects all Americans. They include rules that set limits for pollutants that can harm human health, such as ozone, particulate matter and volatile organic carbon. Zeldin wrote on March 12, 2025, that his deregulation moves would “roll back trillions in regulatory costs and hidden “taxes” on U.S. families.“ What Zeldin didn’t say is that the economic and health benefits from decades of federal clean air regulations have far outweighed their costs. Some estimates suggest every $1 spent meeting clean air rules has returned $10 in health and economic benefits.

How far America has come, because of regulations

In the early 1970s, thick smog blanketed American cities and acid rain stripped forests bare from the Northeast to the Midwest. Air pollution wasn’t just a nuisance – it was a public health emergency. But in the decades since, the United States has engineered one of the most successful environmental turnarounds in history. Thanks to stronger air quality regulations, pollution levels have plummeted, preventing hundreds of thousands of deaths annually. And despite early predictions that these regulations would cripple the economy, the opposite has proven true: The U.S. economy more than doubled in size while pollution fell, showing that clean air and economic growth can – and do – go hand in hand. The numbers are eye-popping. An Environmental Protection Agency analysis of the first 20 years of the Clean Air Act, from 1970 to 1990, found the economic benefits of the regulations were about 42 times greater than the costs. The EPA later estimated that the cost of air quality regulations in the U.S. would be about US$65 billion in 2020, and the benefits, primarily in improved health and increased worker productivity, would be around $2 trillion. Other studies have found similar benefits. That’s a return of more than 30 to 1, making clean air one of the best investments the country has ever made.

Science-based regulations even the playing field

The turning point came with the passage of the Clean Air Act of 1970, which put in place strict rules on pollutants from industry, vehicles and power plants. These rules targeted key culprits: lead, ozone, sulfur dioxide, nitrogen oxides and particulate matter – substances that contribute to asthma, heart disease and premature deaths. An example was the removal of lead, which can harm the brain and other organs, from gasoline. That single change resulted in far lower levels of lead in people’s blood, including a 70% drop in U.S. children’s blood-lead levels.

The results have been extraordinary. Since 1980, emissions of six major air pollutants have dropped by 78%, even as the U.S. economy has more than doubled in size. Cities that were once notorious for their thick, choking smog – such as Los Angeles, Houston and Pittsburgh – now see far cleaner air, while lakes and forests devastated by acid rain in the Northeast have rebounded.

And most importantly, lives have been saved. The Clean Air Act requires the EPA to periodically estimate the costs and benefits of air quality regulations. In the most recent estimate, released in 2011, the EPA projected that air quality improvements would prevent over 230,000 premature deaths in 2020. That means fewer heart attacks, fewer emergency room visits for asthma, and more years of healthy life for millions of Americans.

The economic payoff

Critics of air quality regulations have long argued that the regulations are too expensive for businesses and consumers. But the data tells a very different story. EPA studies have confirmed that clean air regulations improve air quality over time. Other studies have shown that the health benefits greatly outweigh the costs. That pays off for the economy. Fewer illnesses mean lower health care costs, and healthier workers mean higher productivity and fewer missed workdays. The EPA estimated that for every $1 spent on meeting air quality regulations, the United States received $9 in benefits. A separate study by the non-partisan National Bureau of Economic Research in 2024 estimated that each $1 spent on air pollution regulation brought the U.S. economy at least $10 in benefits. And when considering the long-term impact on human health and climate stability, the return is even greater.

The next chapter in clean air

The air Americans breathe today is cleaner, much healthier and safer than it was just a few decades ago. Yet, despite this remarkable progress, air pollution remains a challenge in some parts of the country. Some urban neighborhoods remain stubbornly polluted because of vehicle emissions and industrial pollution. While urban pollution has declined, wildfire smoke has become a larger influence on poor air quality across the nation. That means the EPA still has work to do. If the agency works with environmental scientists, public health experts and industry, and fosters honest scientific consensus, it can continue to protect public health while supporting economic growth. At the same time, it can ensure that future generations enjoy the same clean air and prosperity that regulations have made possible. By instead considering retracting clean air rules, the EPA is calling into question the expertise of countless scientists who have provided their objective advice over decades to set standards designed to protect human lives. In many cases, industries won’t want to go back to past polluting ways, but lifting clean air rules means future investment might not be as protective. And it increases future regulatory uncertainty for industries. The past offers a clear lesson: Investing in clean air is not just good for public health – it’s good for the economy. With a track record of saving lives and delivering trillion-dollar benefits, air quality regulations remain one of the greatest policy success stories in American history. This article, originally published March 12, 2025, has been updated with the administration’s offer of exemptions for industries. Richard E. Peltier, Professor of Environmental Health Sciences, UMass Amherst This article is republished from The Conversation under a Creative Commons license. Read the original article.