Costa Rica sits on the Pacific Ring of Fire, home to more than a dozen volcanoes — five of them considered active. Poás, Turrialba, Irazú, Rincón de la Vieja, and Arenal all have the potential to erupt, and in recent years several have done exactly that. But what do those color-coded alerts actually mean? Whether you’re a resident or a traveler, understanding Costa Rica’s volcanic warning system could one day make all the difference.
Who Issues the Alerts?
Costa Rica uses a two-agency approach to volcanic monitoring and emergency management. OVSICORI-UNA (Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional) is the country’s primary scientific monitoring body. Staffed by volcanologists, seismologists, and atmospheric chemists, it tracks seismic activity, gas emissions, ground deformation, and eruption data around the clock.
When OVSICORI’s data indicates elevated risk, the CNE (Comisión Nacional de Prevención de Riesgos y Atención de Emergencias — National Emergency Commission) translates that scientific assessment into official public alerts. The CNE coordinates with local governments, SINAC (the national parks authority), health officials, and emergency services. Together, these two bodies form the backbone of Costa Rica’s volcanic early warning infrastructure.
The Four-Level Alert Scale
OVSICORI uses a four-level alert system, numbered 1 through 4 and color-coded green, yellow, orange, and red. Each level reflects both scientific observations and the corresponding risk to people and communities. The CNE mirrors this scale when issuing public advisories, sometimes applying different alert levels to different geographic zones depending on proximity to the volcano and current wind and lahar patterns.
Level 1 Green — Normal / Active Monitoring
A green alert means the volcano is in its baseline state. There may be some low-level activity — minor fumarolic emissions, small seismic tremors, or the occasional whiff of sulfur — but nothing that poses an immediate risk to nearby communities. Scientists are monitoring, as they always are, but conditions are stable.
What You Might See
- Routine steam or gas plumes at the crater
- Background seismicity within normal ranges
- No notable changes in ground deformation
What It Means for You
- National parks typically open to visitors
- No special precautions required
- Standard park rules and safety guidelines apply
Most of Costa Rica’s active volcanoes spend the majority of their time at Level 1. Arenal, for example, has been at or near this level since its last major eruptive cycle wound down around 2010.
Level 2 Yellow — Warning / Increased Activity
Yellow indicates that OVSICORI has detected a meaningful uptick in volcanic activity — something beyond the normal baseline. This might include more frequent or stronger seismic swarms, increased gas output, rising temperatures in the crater lake, or early signs of ground inflation that suggest pressure is building below the surface. The situation warrants close attention.
What Scientists Are Seeing
- Minor eruptions or strong bubbling in crater lakes
- Increased emissions of acid gases (SO₂, H₂S)
- Seismic swarms or elevated tremor levels
- Slight inflation of the volcanic edifice
Public Guidance
- Communities near the volcano should monitor official updates
- Intermittent ashfall or gas odors possible in nearby cantons
- Wear an N95 mask if you detect sulfur odors outdoors
- Keep water sources covered; limit outdoor exposure
In April 2025, several cantons surrounding Poás — including Alajuela, Zarcero, Naranjo, and Poás itself — were placed under yellow alert as ash and gas dispersed outward from more intense activity at the crater, even while the crater zone held a higher alert level.
Level 3 Orange — Caution / Significant Concern
Orange is where things become serious. Level 3 means scientists are observing significant volcanic unrest — active eruptions, substantial ash columns, high gas emissions, and possibly signs of magmatic fluids nearing the surface. This is the second-highest level on the four-point scale, and it typically triggers strict access restrictions and heightened emergency readiness.
Indicators at This Level
- Active eruptions with ash plumes (often hundreds of meters to 1+ km)
- High sulfur dioxide emissions (hundreds to thousands of tons/day)
- Elevated seismicity and infrasound
- Possible ejection of incandescent rocks or blocks
- Lahar risk elevated along downstream rivers
What Authorities Do
- National park closure likely or already in effect
- Restricted zones enforced by SINAC and MINAE
- CNE activates contingency plans for affected communities
- Health officials on alert; clinics prepare for respiratory cases
- Aviation Color Code typically set to Orange
Poás spent much of early-to-mid 2025 at Alert Level 3, during which OVSICORI volcanologist Geoffroy Avard cautioned that the situation represented “a new scenario for Poás” — one without clear historical precedent. The third-highest level does not mean danger is imminent for distant communities, but it demands constant vigilance and official coordination.
Level 4 Red — Maximum Emergency
A red alert is the highest level of volcanic emergency in Costa Rica. It means the volcano is producing extreme activity that poses direct, immediate danger — either at the crater itself or potentially to surrounding communities through ashfall, toxic gas clouds, and lahar events. All access to the volcano and its national park is strictly prohibited, and emergency services are fully mobilized.
Conditions at Red Alert
- Large eruptions with ash columns reaching kilometers into the sky
- Significant ashfall affecting multiple cantons
- Extreme gas emissions creating toxic air conditions
- High probability of lahars along river corridors
- Possible danger to aviation in the region
Required Actions
- Entry to Poás Volcano National Park strictly prohibited
- Follow CNE evacuation or shelter-in-place directives
- Stay indoors; seal windows and doors with damp cloths
- Wear N95 masks if ash or gas is present outside
- Avoid all rivers and waterways in the affected zone
- Monitor OVSICORI and CNE official channels only
The CNE issued a Red Alert for Poás Volcano National Park on April 23, 2025, following eruptions that sent ash plumes as high as 4,500 meters above the crater. This triggered coordinated responses across multiple government agencies and prompted the U.S. Embassy to issue formal advisories to its citizens in Costa Rica.
Aviation Color Codes: A Parallel System
Alongside the four ground-level alert numbers, OVSICORI also maintains an Aviation Color Code — a separate but parallel system that specifically communicates risk to aircraft. The codes run green, yellow, orange, and red, and in most cases they mirror the ground-level alert.
However, they can diverge: a volcano might hold a Level 3 ground alert while its aviation code remains at Orange, as was the case with Poás during much of its 2025 eruptive period, where the ash plumes posed ongoing hazards to flight paths even as community-level conditions fluctuated.
Geographic Zoning: Not Everyone Gets the Same Alert
One of the most important things to understand about Costa Rica’s warning system is that alerts are geographically differentiated.
When Poás erupts, the crater area and national park may be at Level 4 (Red), while the immediately surrounding cantons of Grecia and Sarchí might be at Orange due to ashfall and lahar risk, and more distant communities like Alajuela, Naranjo, or Zarcero could be at Yellow due to gas dispersion and wind-driven ash.
This tiered zoning means residents and travelers need to check the specific alert for their location, not just the headline level assigned to the volcano itself.
Active Volcanoes to Know
Poás
The most closely watched volcano in Costa Rica and the one most likely to be under an elevated alert. Its hyper-acidic crater lake, Laguna Caliente, drives frequent phreatomagmatic eruptions. Currently under active monitoring following sustained activity throughout 2025.
Turrialba
Located in Cartago Province and periodically active, Turrialba has intermittently disrupted operations at Juan Santamaría International Airport with ash emissions. It’s been relatively quieter in recent years but remains under continuous monitoring.
Irazú
The highest active volcano in Costa Rica at 3,432 meters. Its last major eruption cycle ran from 1963–1965, but it remains geologically active. Generally considered stable and open to visitors, though OVSICORI maintains ongoing surveillance.
Rincón de la Vieja
In Guanacaste Province, this volcano regularly produces minor phreatic eruptions and is known for its mud pots and fumaroles. Visitors to the national park should always check current alert status before heading to the crater area.
Arenal
Costa Rica’s most iconic volcanic cone, Arenal was one of the most active volcanoes in the world during its 1968–2010 eruptive period. It has since entered a relatively quiet phase, though it is still considered active and monitored continuously.
Staying Informed: Official Sources
During any period of elevated volcanic activity, the only reliable sources of alert information are official ones. Social media rumors and secondhand reports spread quickly but are often inaccurate. For verified, real-time information, turn to:
OVSICORI-UNA — Scientific monitoring, eruption reports, alert level changes
CNE (National Emergency Commission) — Official public alerts, evacuation orders, community guidance
SINAC (National Parks System) — Park status, access restrictions, temporary closures
U.S. Embassy Costa Rica — Advisories for U.S. citizens and international travelers
Traveler’s Quick Checklist
Before visiting any active volcano in Costa Rica, take these simple steps:
- Check the current alert level for your specific destination on OVSICORI or SINAC
- Confirm national park access — closures can happen with little advance notice
- Pack an N95 mask, especially if visiting during periods of elevated activity
- Know which rivers to avoid in the surrounding area (lahar risk zones)
- Have a flexible itinerary — volcanic conditions can change within hours