The United States is home to more active volcanoes than most people realize. The U.S. Geological Survey monitors more than 160 potentially active volcanoes in the United States and its territories, including in Hawaii, Alaska, Washington, Oregon, and California. Several of these — including Kīlauea in Hawaii and Mount St. Helens in Washington — have demonstrated the power of volcanic activity to reshape landscapes and threaten communities. Ready.gov’s Volcano Hazard Information Sheet provides essential guidance for people who live near or visit volcanic areas.
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Types of Volcanic Hazards
Lava Flows
Molten rock that flows from a volcanic vent. Most lava flows move slowly enough to be outrun on foot, but they incinerate everything in their path and cannot be stopped. Lava flows are a primary hazard on the Big Island of Hawaii.
Pyroclastic Flows
The most deadly volcanic hazard. A pyroclastic flow is a fast-moving current of hot gas, ash, and volcanic rock that can reach speeds of 700 mph and temperatures of 1,800°F. There is no surviving a direct pyroclastic flow encounter — evacuation is the only protection.
Ashfall
Volcanic ash is composed of tiny shards of glass and minerals. Even small amounts can collapse roofs, damage engines, contaminate water supplies, disrupt aviation across vast regions, and cause respiratory illness. Volcanic ash can fall hundreds to thousands of miles from the eruption site.
Volcanic Gases
Eruptions release sulfur dioxide (SO₂), hydrogen sulfide (H₂S), carbon dioxide (CO₂), and other toxic gases. Near an active eruption, these gases can reach lethal concentrations.
Lahars (Volcanic Mudflows)
A lahar is a mixture of volcanic debris and water that behaves like wet concrete and can travel at 40 mph. Lahars can travel far from the eruption site along river valleys, destroying everything in their path.
Before a Volcanic Eruption: Preparation
- Know your volcanic hazard zone. USGS and your state emergency management agency publish volcanic hazard zone maps. Know which hazards are most likely at your specific location.
- Have an evacuation plan. Know multiple routes out of your area and the locations of evacuation shelters designated by your county emergency management office.
- Prepare for ashfall specifically. Have N95 or P100 respirators for every household member (surgical masks are not adequate). Have goggles, long sleeves, and caps to protect skin. Have sealed food and water supplies. Know how to protect your HVAC system by turning it off during heavy ashfall.
- Protect your water supply. Volcanic ash can contaminate open water sources. Store water for at least 72 hours and know how to access backup water sources.
- Sign up for alerts from your volcano observatory. The USGS Volcano Hazards Program (volcanoes.usgs.gov) issues volcano alert level notifications from Normal through Warning.
During a Volcanic Eruption
- If told to evacuate, leave immediately — do not wait to see what happens
- Follow designated evacuation routes — do not try shortcuts through unknown terrain
- If caught in ashfall: wear your respirator, cover all skin, avoid driving if possible, drive slowly with headlights on if you must
- Stay indoors during heavy ashfall, close all windows and doors, and turn off HVAC systems
- Avoid low-lying areas and drainages — lahar risk increases during and after eruptions
After an Eruption
- Wait for official all-clear before returning to evacuated areas
- Ash cleanup requires respirators — ash is heavy when wet and can collapse roofs
- Check water supplies before drinking — have water tested after volcanic events
- Be aware of continued volcanic activity — eruptions often occur in phases over days, weeks, or months
How PubSafe Supports Volcanic Emergency Response
Volcanic emergencies often unfold over extended periods — sometimes days or weeks — requiring sustained community coordination. PubSafe provides a resilient communication platform that helps communities stay connected during extended evacuation periods, coordinating accommodations, supply sharing, and welfare checks. PubSafe enables real-time information sharing about ashfall accumulation, road conditions, and access to resources, and helps connect displaced residents with shelter, food, and housing assistance. In the 2018 Kīlauea eruption that displaced thousands of Big Island residents for months, long-term community coordination was essential. PubSafe’s platform is designed for exactly this kind of sustained emergency community management.
Resources
- Ready.gov Volcanoes page
- USGS Volcano Hazards Program: volcanoes.usgs.gov
Download the Ready.gov Volcano Hazard Information Sheet and know your volcanic hazard zone. Connect your community on PubSafe.
Volcanic Smog (Vog) and Long-Term Air Quality Impacts
Volcanic eruptions affect air quality far beyond the immediate eruption zone, sometimes across entire island chains or regional areas. One of the most important long-term air quality impacts of volcanic activity is the creation of volcanic smog, commonly known as “vog.” Vog is a form of air pollution created when sulfur dioxide (SO₂) and other volcanic gases react with oxygen, moisture, and sunlight to form fine particles and aerosols — primarily sulfuric acid and sulfate compounds.
In Hawaii, where Kīlauea has been erupting nearly continuously for decades, vog is a persistent regional air quality concern. It can affect communities hundreds of miles from the eruption vent, depending on wind direction and atmospheric conditions. Symptoms of vog exposure include headache, sore throat, eye irritation, and worsening of respiratory conditions including asthma. People with respiratory or cardiovascular conditions, children, and the elderly are most vulnerable to vog-related health impacts.
Hawaii’s Department of Health monitors SO₂ and particulate matter concentrations from volcanic emissions and issues Air Quality Index (AQI) advisories based on measured vog conditions. The site vog.ivhhn.org provides real-time vog monitoring data and forecasts for the Hawaiian Islands. If you live in an area affected by vog, monitor air quality forecasts, keep windows and doors closed on high-vog days, use HEPA air filtration indoors, and follow your healthcare provider’s guidance if you have pre-existing respiratory conditions.
Volcanic Ash: A Global Aviation Hazard
Volcanic ash is not just a local hazard — it poses a significant threat to aviation across vast geographic areas. Jet engines are designed to operate in clean air and are extremely vulnerable to volcanic ash, which can melt inside the engine’s turbine section (ash melting point is below the temperature of a jet engine combustion chamber), coat and erode compressor blades, clog fuel nozzles, and block air pressure sensing instruments. Multiple incidents of jet engine flameouts and near-accidents caused by volcanic ash encounters have prompted the aviation industry to develop sophisticated volcanic ash avoidance systems.
The 2010 eruption of Eyjafjallajökull in Iceland produced an ash cloud that closed European airspace for six days, stranding 10 million passengers and costing airlines an estimated $1.3 billion in lost revenue. More recently, eruptions in Alaska, the Aleutian Islands, and Central America have periodically caused flight route adjustments and cancellations affecting U.S. travelers. The Washington Volcanic Ash Advisory Center (VAAC), operated by NOAA’s Aviation Weather Center, monitors volcanic ash clouds in the U.S. airspace area and issues advisories to the aviation industry.
For travelers, volcanic ash events can cause significant travel disruption with little warning. Build flexibility into travel plans involving volcanic regions, follow your airline’s guidance about rebooking options, and monitor volcano observatory alerts for destinations and connecting hub airports in volcanic regions. And connect your community on PubSafe — because whether you are traveling through volcanic regions or sheltering in place during an eruption, connected communities navigate these complex emergencies more effectively than isolated households.
