Central American Volcanoes Explained: Guatemala, Nicaragua, Costa Rica and the Volcanic Arc

What Are Central American Volcanoes?

Central American volcanoes are volcanic systems associated mainly with the tectonic boundary running along the Pacific side of the Central American isthmus.

The principal volcanic chain extends through:

• Guatemala
• El Salvador
• Honduras
• Nicaragua
• Costa Rica
• Western Panama

The arc also connects tectonically with the volcanic regions of southern Mexico, including the cross-border Tacaná volcanic complex between Mexico and Guatemala.

Not every mountain in Central America is volcanic, and not every volcano forms a perfect cone. The region contains:

• Composite volcanoes and stratovolcanoes
• Large calderas
• Lava-dome complexes
• Shield volcanoes
• Volcanic crater lakes
• Monogenetic cone fields
• Maar craters
• Fissure-fed lava fields
• Geothermal and hydrothermal systems

Many volcanic summits rise above fertile agricultural regions, major cities, highways, airports and densely inhabited valleys. This combination of active volcanoes and concentrated populations makes Central America one of the world’s most important regions for volcanic-risk research.

The Central American Volcanic Arc

The Central American Volcanic Arc is a long but segmented belt of volcanoes extending along the Pacific side of the isthmus.

From northwest to southeast, the arc includes volcanic systems in Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica and Panama. Its morphology changes considerably between countries because the geometry of the subducting plate, the thickness of the overriding crust and the local fault network are not uniform.

Part of the Pacific Ring of Fire

The arc forms part of the broader Pacific Ring of Fire, the discontinuous belt of subduction zones, earthquakes and volcanoes surrounding much of the Pacific Ocean.

However, the Ring of Fire is not one connected geological structure. The Central American arc is specifically controlled by tectonic processes along the Middle America Trench and the surrounding Caribbean plate boundary.

How Did Central American Volcanoes Form?

Most Central American volcanism is generated by subduction. The dense oceanic Cocos Plate moves beneath the lighter Caribbean Plate along the Middle America Trench.

1. Oceanic crust enters the mantle

The Cocos Plate carries oceanic crust, sediments, hydrated minerals and trapped water into the subduction zone.

2. Water is released from the slab

As temperature and pressure increase, water and other volatile substances are released from minerals within the descending plate.

3. Mantle rock partially melts

Fluids rise into the overlying mantle wedge and lower the temperature at which parts of the mantle begin to melt.

4. Magma rises into the crust

The resulting magma is less dense than the surrounding rock. It rises through fractures and may accumulate in crustal reservoirs beneath the volcanic arc.

5. Magma evolves

While stored in the crust, magma may cool, crystallize, mix with new magma or assimilate surrounding rock. These processes can produce basaltic, andesitic, dacitic and rhyolitic compositions.

6. An eruption begins

If magma pressure exceeds the strength of the surrounding rock, it can fracture the crust and move toward the surface through conduits, dikes and fissures.

Learn more about these processes in

Volcano Science Explained
.

Why many eruptions are explosive

Central American magma commonly contains substantial dissolved water and other gases. Andesitic and dacitic magma can also be relatively viscous.

As magma rises and pressure decreases, dissolved gas forms expanding bubbles. If the gas cannot escape efficiently, pressure may build until the magma fragments violently.

This process can generate:

• Ash columns
• Volcanic bombs
• Pyroclastic density currents
• Lava-dome explosions
• Widespread pumice deposits

Why Is the Volcanic Chain Discontinuous?

Central America does not contain one perfectly continuous row of equally spaced volcanoes. Volcanism is concentrated into segments separated by gaps or areas with fewer young volcanic centers.

These differences reflect changes in:

• The angle of the descending Cocos Plate
• The age and composition of the oceanic crust
• The thickness of the overriding plate
• The presence of oceanic ridges and fracture zones
• Regional faults within the Caribbean Plate
• The location of crustal magma reservoirs

In Honduras, for example, the main active volcanic chain is less prominent than in neighboring Guatemala, El Salvador and Nicaragua. Nevertheless, Honduras contains Holocene volcanic centers around Lake Yojoa and the Gulf of Fonseca.

Farther southeast, the volcanic arc becomes more complex in Panama as the tectonic setting transitions toward the plate boundaries of northwestern South America.

Volcanoes of Guatemala

Guatemala contains one of the most dramatic concentrations of volcanoes in Central America. A chain of steep cones runs roughly parallel to the Pacific coast, overlooking highland cities, coffee plantations and heavily populated valleys.

Important Guatemalan volcanoes include:

• Fuego
• Acatenango
• Agua
• Pacaya
• Santa María and Santiaguito
• Tacaná
• Tajumulco
• Atitlán
• Tolimán
• San Pedro
• Almolonga and Cerro Quemado
• Suchitán
• Moyuta

Fuego

Volcán de Fuego is one of Central America’s most persistently active stratovolcanoes. Its activity commonly includes explosions, incandescent ejecta, ash plumes, lava flows and pyroclastic density currents.

Deep ravines radiating from the summit channel hot volcanic material and rain-generated lahars toward communities and infrastructure around the volcano.

Acatenango

Acatenango forms a massive volcanic complex immediately north of Fuego. Although it is quieter than its neighbor, it remains geologically connected to the broader volcanic landscape.

Its summit is a popular viewpoint for observing Fuego, creating a need for careful attention to weather, altitude, volcanic activity and official restrictions.

Pacaya

Pacaya is a complex volcano south of Guatemala City. Its modern activity has included Strombolian explosions, lava fountains, lava flows and ash emissions.

Lava has repeatedly threatened farms, roads and settlements around the volcanic complex.

Santa María and Santiaguito

Santa María produced a major explosive eruption in 1902. Beginning in 1922, the Santiaguito lava-dome complex began growing within the large crater on Santa María’s southwestern flank.

Dome growth, rockfalls, explosions and partial collapses can generate pyroclastic density currents. Ash and loose volcanic debris are also remobilized by tropical rainfall into lahars.

Tacaná

Tacaná straddles the Guatemala–Mexico border. It is a large volcanic complex with fumarolic activity and evidence of explosive eruptions.

Lake Atitlán volcanic region

Lake Atitlán occupies part of a large caldera surrounded by the volcanoes Atitlán, Tolimán and San Pedro.

The beautiful landscape records an extremely powerful volcanic history involving large explosive eruptions and caldera collapse.

Volcanoes of El Salvador

El Salvador is sometimes called the Land of Volcanoes. Despite its small area, it contains numerous volcanic cones, calderas, crater lakes and geothermal systems.

Major volcanic systems include:

• Santa Ana, also known as Ilamatepec
• Izalco
• San Salvador volcanic complex
• Ilopango Caldera
• San Miguel, also known as Chaparrastique
• Tecapa
• Chinameca
• Usulután
• Apaneca volcanic range
• Conchagua

Santa Ana

Santa Ana is El Salvador’s highest volcano. Its summit contains multiple nested craters and an acidic crater lake.

Potential hazards include phreatic explosions, ashfall, ballistic blocks, acidic gases and lahars.

Izalco

Izalco formed during historical time on the southern flank of the older Santa Ana volcanic complex. Frequent activity during the eighteenth, nineteenth and twentieth centuries built a steep, dark cone visible from the Pacific.

San Salvador volcanic complex

The San Salvador volcanic complex rises beside the country’s capital and metropolitan region. It contains the Boquerón crater and numerous flank vents.

Its proximity to dense urban development makes even low-probability future activity a major planning concern.

Ilopango Caldera

Lake Ilopango occupies a large caldera east of San Salvador. The system has produced extremely explosive eruptions capable of spreading ash and pyroclastic deposits across broad regions.

Later activity formed lava domes and volcanic islands within the lake.

San Miguel

San Miguel is a steep stratovolcano in eastern El Salvador. It has produced ash emissions, explosions and lava flows during its history.

Volcanoes of Honduras

Honduras does not possess the continuous chain of prominent active stratovolcanoes seen in Guatemala or Nicaragua. Nevertheless, it contains young volcanic centers and fields that belong to the wider Central American tectonic region.

Principal Holocene volcanic areas include:

• Lake Yojoa volcanic field
• Isla del Tigre
• Isla Zacate Grande

Lake Yojoa volcanic field

The Lake Yojoa region contains scoria cones, craters and lava flows along the northern side of the lake.

Its landscape demonstrates that volcanic activity can occur as a distributed field rather than through one dominant central stratovolcano.

Isla del Tigre

Isla del Tigre is a conical volcanic island in the Gulf of Fonseca. The volcano rises steeply above the port town of Amapala.

Isla Zacate Grande

Zacate Grande is an older volcanic structure surrounded by younger cones. It lies within the tectonically complex Gulf of Fonseca, where the territories of Honduras, El Salvador and Nicaragua approach one another.

The relative quietness of Honduran volcanoes does not eliminate geological risk. Earthquakes, landslides, geothermal activity and poorly documented volcanic histories remain relevant to hazard assessment.

Volcanoes of Nicaragua

Nicaragua contains a striking line of volcanic cones and calderas extending from the Gulf of Fonseca toward Lake Nicaragua.

Major systems include:

• Cosigüina
• San Cristóbal volcanic complex
• Telica
• Cerro Negro
• Las Pilas and El Hoyo
• Momotombo
• Apoyeque
• Masaya
• Mombacho
• Concepción
• Maderas

Masaya

Masaya is a large caldera complex southeast of Managua. Its active Santiago crater has repeatedly emitted substantial quantities of volcanic gas and has periodically contained an active lava lake.

Gas pollution can affect communities, agriculture, roads and visitors even when no large explosive eruption is occurring.

Cerro Negro

Cerro Negro is a young cinder cone that first appeared in the nineteenth century. Repeated eruptions rapidly built its black, unvegetated cone.

Activity has included lava fountains, ash columns and lava flows. Strong winds may carry ash across agricultural regions and inhabited areas.

San Cristóbal

San Cristóbal is Nicaragua’s highest volcano and part of a larger volcanic complex. It has produced explosions, ash emissions and gas release.

Telica

Telica is an active volcanic complex with a deep summit crater. Activity commonly involves earthquakes, gas emissions, crater incandescence and intermittent explosions.

Momotombo

Momotombo is a symmetrical stratovolcano near Lake Managua. Its volcanic heat supports geothermal development, while eruptions can generate ashfall, lava and ballistic hazards.

Concepción

Concepción forms the northern half of Ometepe Island in Lake Nicaragua. The steep stratovolcano has produced explosions, ash emissions and lahars.

Apoyeque

Apoyeque is a caldera and volcanic complex on the Chiltepe Peninsula near Managua. Its geological history includes powerful explosive eruptions.

Its proximity to a major urban region makes it an important low-frequency but potentially high-consequence volcanic system.

Volcanoes of Costa Rica

Costa Rica’s volcanic arc is divided among several northwest-to-southeast mountain ranges, including the Guanacaste, Tilarán and Central volcanic cordilleras.

Major volcanoes include:

• Orosí
• Rincón de la Vieja
• Miravalles
• Tenorio
• Arenal
• Platanar
• Poás
• Barva
• Irazú
• Turrialba

Poás

Poás contains a highly active hydrothermal system and an acidic crater lake whose size, temperature and chemistry can change considerably.

The volcano is capable of phreatic and phreatomagmatic explosions that eject water, mud, ash and blocks from the crater.

Turrialba

Turrialba lies east of the densely populated Central Valley. Its modern activity has included gas emissions, ash-producing eruptions and the opening or enlargement of summit vents.

Ash can affect agriculture, water supplies, aviation and communities around San José depending on wind direction.

Rincón de la Vieja

Rincón de la Vieja is a complex volcano in northwestern Costa Rica. Its active crater contains a hot acidic lake and vigorous hydrothermal system.

Explosions may eject lake water and sediment, while material entering river valleys can generate lahars.

Irazú

Irazú is Costa Rica’s highest active volcano. Its eruption between 1963 and 1965 produced persistent ashfall that affected San José and surrounding agricultural regions.

Arenal

Arenal was considered quiet until a destructive eruption began in 1968. Activity continued for decades, involving explosions, lava flows, glowing avalanches and pyroclastic currents.

Its subsequent quiet phase does not mean the volcano is extinct.

Miravalles and geothermal energy

The Miravalles region contains an important geothermal field. Wells tap hot fluids circulating through fractured volcanic rock to produce electricity.

Volcanoes of Panama

Volcanism in Panama is less continuously active than in Nicaragua or Costa Rica, but western Panama contains geologically young volcanic systems.

The most important include:

• Volcán Barú
• La Yeguada volcanic complex
• El Valle volcanic complex

Volcán Barú

Barú is Panama’s highest mountain and a large stratovolcano near Boquete and Volcán in Chiriquí Province.

Geological evidence indicates explosive eruptions, pyroclastic flows and lahars during its past. Its forested appearance and lack of recent historical eruptions should not be confused with extinction.

La Yeguada

La Yeguada is a volcanic complex containing domes, craters and young volcanic deposits. It lies in a region of forests, farms and hydroelectric infrastructure.

El Valle volcanic complex

El Valle de Antón occupies a large volcanic depression associated with an older caldera system.

Although the landscape is now heavily eroded and populated, hot springs and volcanic deposits preserve evidence of its magmatic and hydrothermal history.

Major Central American Volcanoes

Eruption Styles and Volcanic Landforms

Central American volcanoes display a broad range of eruptive behavior. Individual volcanoes may also change eruption style as magma composition, gas pressure and conduit conditions evolve.

Strombolian eruptions

Strombolian activity consists of repeated bursts that throw incandescent lava fragments above the crater.

Pacaya, Fuego and Cerro Negro have produced this style of activity, sometimes accompanied by lava flows and larger explosions.

Vulcanian eruptions

Vulcanian eruptions are short, powerful explosions caused when pressurized gas breaks through a blocked or viscous conduit.

They can generate dense ash plumes, ballistic blocks and pyroclastic currents.

Plinian eruptions

Large gas-rich eruptions can sustain ash columns reaching high into the atmosphere. Column collapse may produce widespread pyroclastic density currents.

Past eruptions at Santa María, Ilopango, Atitlán and other caldera systems demonstrate the arc’s capacity for very large explosive events.

Lava-dome growth

Viscous magma can accumulate above a vent as a lava dome. Domes may grow slowly, but unstable portions can collapse with little warning.

Santiaguito is the region’s best-known example of long-lived dome growth.

Phreatic eruptions

Phreatic eruptions occur when groundwater or crater-lake water is suddenly heated and converted into steam.

These explosions may eject mud, altered rock, ash and ballistic blocks without bringing significant fresh magma to the surface.

Poás and Rincón de la Vieja are especially known for hydrothermal and crater-lake activity.

Caldera-forming eruptions

A caldera may form when the ground collapses after a large volume of magma is erupted or withdrawn from beneath a volcano.

Ilopango, Atitlán, Masaya and other Central American systems preserve evidence of major collapse events.

Learn more in

Calderas Explained
.

Cinder cones and fissures

Some eruptions occur through fissures or create relatively small cones composed of loose scoria and ash.

Cerro Negro demonstrates how repeated eruptions can build a new cone rapidly within a larger volcanic field.

Compare these structures in

Volcano Types Explained
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Major Hazards from Central American Volcanoes

Volcanic risk across Central America is intensified by steep terrain, tropical rainfall, dense populations, vulnerable infrastructure and communities built on or beside old volcanic deposits.

Explore each process in

Volcanic Hazards Explained
.

Ashfall

Volcanic ash consists of fine fragments of rock, minerals and glass. Wind can carry it far beyond the volcano.

Ashfall may:

• Reduce visibility
• Disrupt aviation
• Damage crops and pasture
• Contaminate drinking water
• Irritate eyes and lungs
• Damage engines and machinery
• Interrupt electricity and communications
• Overload roofs when deposits become thick or wet

Pyroclastic density currents

Pyroclastic density currents are hot, fast-moving mixtures of volcanic gas, ash and rock.

They can form when eruption columns collapse, lava domes fail or explosive material spills over a crater rim.

Valleys around Fuego and Santiaguito repeatedly channel these destructive currents.

Lahars

Lahars form when water mixes with volcanic ash, rock and soil. In tropical Central America, heavy rain can generate lahars during an eruption or long afterward.

Lahars may travel through river channels far beyond the summit and can bury roads, bridges, farms and settlements.

Read the dedicated guide:

Lahars Explained
.

Lava flows

Lava flows usually move more slowly than pyroclastic currents, but they can destroy homes, farms, roads and power infrastructure.

Flank vents may allow lava to emerge closer to populated areas than expected from the summit alone.

Ballistic projectiles

Explosions can throw blocks and volcanic bombs around the crater. These projectiles pose an immediate danger to visitors, climbers, guides and monitoring teams.

Volcanic gases

Volcanoes release sulfur dioxide, carbon dioxide, hydrogen sulfide, water vapor and other gases.

Masaya can produce substantial gas pollution even without a major eruption. Acidic gases can damage crops, affect breathing and corrode machinery.

Crater-lake explosions

Acidic crater lakes may become heated by magma and volcanic gas. Sudden explosions can eject water, mud and rock while generating surges around the crater.

Debris avalanches and flank collapse

Large volcanic edifices may be weakened by faults, hydrothermal alteration, earthquakes and magma intrusion.

Collapse of a volcanic flank can produce a massive debris avalanche and redirect rivers across surrounding lowlands.

Earthquakes

Central America experiences both volcanic earthquakes and powerful tectonic earthquakes generated by the regional plate boundaries.

Earthquakes can destabilize volcanic slopes, damage monitoring equipment and complicate evacuations during unrest.

Major Historic Eruptions in Central America

Ilopango, El Salvador

Ilopango has produced several major explosive eruptions. Its Tierra Blanca Joven eruption dispersed widespread ash and pumice and generated pyroclastic flows across a large area of El Salvador.

Cosigüina, Nicaragua — 1835

Cosigüina produced a powerful explosive eruption in 1835. Ash spread across Central America, the Caribbean and adjacent regions.

Santa María, Guatemala — 1902

Santa María’s 1902 eruption was one of the largest eruptions of the twentieth century. It generated a towering ash column and devastated areas around the volcano.

Santiaguito, Guatemala — from 1922

The Santiaguito lava-dome complex began growing inside the 1902 crater and has remained intermittently active for more than a century.

Irazú, Costa Rica — 1963–1965

Irazú produced prolonged ashfall affecting San José, agriculture, water systems and transportation. Rain remobilized volcanic debris and generated destructive mudflows.

Arenal, Costa Rica — 1968

Arenal reactivated violently in July 1968. Explosions and pyroclastic activity destroyed communities on the volcano’s western side and initiated decades of activity.

Cerro Negro, Nicaragua — 1992

Cerro Negro’s 1992 eruption produced widespread ashfall that damaged crops, contaminated water and affected communities across western Nicaragua.

Santa Ana, El Salvador — 2005

Santa Ana erupted explosively in October 2005, ejecting ash and blocks from its summit crater. Heavy rain associated with a tropical weather system compounded regional landslide and lahar hazards.

Fuego, Guatemala — 2018

A major eruption of Fuego in June 2018 generated pyroclastic density currents that descended populated ravines and caused catastrophic loss of life.

The disaster demonstrated how rapidly pyroclastic currents can move and why settlements inside mapped hazard corridors face extreme risk.

Explore other landmark events in

Historic Volcanic Eruptions
.

How Are Central American Volcanoes Monitored?

Volcano monitoring is conducted by national geological, meteorological and academic institutions, often supported by regional and international scientific partnerships.

Seismic monitoring

Seismometers detect earthquakes caused by fracturing rock, moving magma, volcanic gas and hydrothermal fluids.

Scientists examine earthquake frequency, depth, location and waveform to identify changes beneath a volcano.

Ground deformation

Magma entering or leaving a reservoir may cause the ground to rise, sink or tilt.

Deformation can be measured with:

• Continuous GPS
• Tiltmeters
• Electronic distance measurements
• Satellite radar interferometry

Gas monitoring

Changes in sulfur dioxide, carbon dioxide and other gases may indicate movement or depressurization of magma.

Ground instruments, drones, aircraft and satellites may all contribute gas data.

Thermal monitoring

Infrared cameras and satellites detect heat from lava, crater lakes, lava domes, fumaroles and active vents.

Crater-lake monitoring

At volcanoes such as Poás and Rincón de la Vieja, scientists monitor lake temperature, acidity, chemistry, water level and gas release.

Visual cameras

Permanent cameras help observatories detect ash plumes, explosions, dome growth, lava flows and changing crater conditions.

Rain and lahar sensors

Rain gauges, acoustic-flow monitors and river observations can provide warnings when volcanic debris begins moving through channels.

Satellite observations

Satellites can identify:

• Ash clouds
• Sulfur dioxide
• Thermal anomalies
• Ground deformation
• New lava flows
• Changes in crater lakes

Learn how these datasets are combined in

Volcano Monitoring and Forecasting Explained
.

Volcano Observatories and Official Agencies

During unrest, information should come from the scientific institution and civil-protection agency responsible for the volcano.

• Guatemala: INSIVUMEH monitors volcanoes, earthquakes, weather and lahars.
• El Salvador: the national environmental and civil-protection institutions monitor volcanic and seismic activity.
• Nicaragua: INETER monitors volcanoes, earthquakes and other geological hazards.
• Costa Rica: OVSICORI-UNA and the Red Sismológica Nacional monitor volcanic and seismic activity.
• Panama: national institutions and university-based seismic networks contribute to geological monitoring and hazard assessment.

Alert-level systems and terminology differ among countries. A color or warning category must therefore be interpreted according to the definitions used by the issuing authority.

Living Near Central American Volcanoes

Millions of people live within volcanic landscapes because these regions provide fertile soil, water, geothermal energy, tourism opportunities and favorable highland climates.

Coffee, maize, vegetables, fruit and other crops are widely grown on volcanic soils. Yet farms and settlements may also occupy lahar channels, old lava flows and pyroclastic deposits.

Know the hazard map

A volcanic hazard map shows areas that may be affected by lava, ash, pyroclastic flows, lahars, landslides or ballistic projectiles.

Residents should know whether their homes, schools, farms and workplaces lie within mapped hazard corridors.

Recognize river hazards

During heavy rain, a river draining an active volcano may suddenly carry volcanic mud and debris.

Rumbling sounds, rapidly rising water or a sudden change in river color can indicate an approaching lahar. People should move away from channels and toward high ground according to official instructions.

Prepare for ashfall

Useful preparations may include:

• Respiratory protection
• Eye protection
• Covered water and food
• Protected machinery and electronics
• Vehicle and generator filters
• Plans for livestock and pets
• Safe methods for removing ash from roofs

Respect exclusion zones

Crater rims and active lava areas may appear accessible during quiet periods. Sudden explosions, toxic gases, unstable ground and ballistic blocks can make these zones deadly.

Follow official warnings

Dramatic videos do not reveal the full condition of a volcano. Cloud cover may hide dangerous activity, while harmless steam can sometimes appear more alarming than it is.

Official observatories interpret multiple data streams rather than relying on one image or eyewitness report.

Volcano Tourism and Safety

Volcano tourism is economically important in Guatemala, Nicaragua, Costa Rica and Panama. Popular destinations include Acatenango, Pacaya, Masaya, Cerro Negro, Poás, Irazú, Arenal and Barú.

A volcano being open to visitors does not mean that it is free of danger. Conditions may change rapidly because of:

• Explosions
• Gas emissions
• Rockfalls
• Lightning
• Heavy rain
• Flash floods
• Altitude illness
• Rapid temperature changes

Visitors should use authorized trails, follow park closures and avoid entering restricted crater or lava-flow areas.

Tropical Rainfall and Volcanic Risk

Central America’s tropical climate has a major influence on volcanic hazards.

Rain-triggered lahars

Ash and loose pyroclastic debris deposited during an eruption can remain unstable for years. Heavy rain repeatedly washes this material into ravines and rivers.

Hurricanes and tropical storms

Tropical storms may produce intense rainfall across volcanic terrain, generating lahars and landslides even when the volcano itself is not erupting.

Rapid vegetation recovery

Tropical vegetation can quickly cover old volcanic deposits. A forested valley may therefore conceal evidence of previous pyroclastic flows or lahars.

Acid rain and gas

Sulfur dioxide reacts in the atmosphere to form acidic aerosols and precipitation. Persistent degassing may damage plants, metal structures and water supplies downwind.

Why Central American Volcanoes Matter

The Central American Volcanic Arc is a natural laboratory for studying subduction, magma generation, explosive eruptions and volcanic risk.

It contains examples of:

• Persistently active stratovolcanoes
• Long-lived lava domes
• Young cinder cones
• Acidic crater lakes
• Large calderas
• Geothermal fields
• Volcanoes beside major cities
• Rain-driven lahars
• International ash and aviation hazards

The region also demonstrates why eruption size alone does not determine disaster severity.

A moderate eruption may become catastrophic when pyroclastic flows enter a populated ravine. A small crater explosion can kill visitors standing nearby. A thin ash deposit can cause major losses if it falls on vulnerable crops during the growing season.