Irazú: The Thunder of the Highlands

Standing tall above the colonial city of Cartago, Irazú Volcano (Volcán Irazú) is the highest active volcano in Costa Rica, reaching an elevation of 3,432 meters (11,260 feet). Its name is derived from the indigenous word Iztarú, meaning “Mountain of Thunder and Tremors”—a fitting title for a giant that has periodically shaken the Central Valley for centuries.

Unlike the perfect cone of Arenal regarding which usually appears on postcards, Irazú is a sprawling, shield-like stratovolcano that dominates the horizon with its massive bulk. It is most famous for two things: the stunning, alien-green crater lake at its summit, and the historic eruption of 1963, which turned a state visit by US President John F. Kennedy into a gritty, ash-covered affair.

On a clear day—a rare luxury in the cloud-forest highlands—Irazú offers one of the most spectacular vistas in the Americas. From its windswept peak, it is possible to see both the Atlantic Ocean (Caribbean Sea) to the east and the Pacific Ocean to the west simultaneously, a testament to the narrow, rugged spine of the Central American isthmus.

The Diego de la Haya Crater

The summit of Irazú is a moonscape of grey ash and black rock, hosting several craters. The main attraction, however, is the Diego de la Haya crater.

The Acid Lake

Nestled 300 meters deep within this crater lies a lake that changes color like a mood ring.

• The Color: It is typically a brilliant, milky emerald green or turquoise. This color comes from rainfall dissolving minerals (sulphur, carbonates, and magnesium) from the crater walls.
• The Chemistry: It is highly acidic and cold. No fish swim here; it is a chemical soup.
• Variability: The lake is ephemeral. In dry years, it can shrink to a muddy red puddle or evaporate entirely, transforming into a dry, dusty bowl. But when the rains return, the jewel reappears.

The Playa Hermosa

Adjacent to the main crater is a vast, flat expanse known as Playa Hermosa (Beautiful Beach). Despite the name, there is no sand and no ocean. It is a terrace of volcanic ash, the remnant of an old crater floor that provides a stark, desolate beauty reminiscent of the surface of Mars.

The Governor’s Volcano: A History of Eruptions

Irazú has a long memory. The first recorded eruption dates back to 1723.

• Diego de la Haya: The eruption was documented by the then-Spanish Governor of Costa Rica, Diego de la Haya Fernández. He wrote detailed reports to the Spanish Crown about the “fire and Brimstone” raining down on the colonial capital of Cartago. In honor of his meticulous chronicling, the active crater bears his name today.
• The Cycle of Ash: Since then, Irazú has erupted roughly every 20 to 40 years. Major events occurred in 1917-1921, 1939-1940, and, of course, the infamous 1963 event.
• 1994 Activity: The last significant activity was a phreatic (steam) explosion in 1994. It opened a new crack on the north flank, sending a small landslide down the river valley. Since then, the giant has been mostly sleeping, emitting only fumarolic gases.

The Day JFK Came to Town (1963-1965)

Irazú has erupted at least 23 times since records began in 1723, but none were as politically timed as the eruption of 1963.

The Historic Visit

In March 1963, John F. Kennedy arrived in San José for a historic summit with the presidents of Central America. He was the first sitting US President to visit Costa Rica.

• The Greeting: Just days before his arrival, Irazú woke up. As JFK’s motorcade drove through the streets of San José, greeted by cheering crowds, a fine rain of volcanic ash was falling from the sky.
• VEI 3: The eruption intensified, sending columns of ash thousands of feet into the air. It didn’t stop when JFK left. It continued for two years, until 1965.

The Aftermath

The eruption was a disaster for the Central Valley.

• Agriculture: The coffee plantations and dairy farms of the fertile highlands were buried under tons of gray dust. The “golden bean” (coffee) crop was decimated. However, in the long run, the ash re-mineralized the soil, making it even more fertile for future generations—a classic volcanic paradox.
• Urban Impact: In San José and Cartago, roofs collapsed under the weight of the water-logged ash. Residents had to wear handkerchiefs over their faces and sweep their sidewalks daily. The city of San José had to mechanically remove 80mm of ash from the roofs of the National Theatre.
• Floods: The ash clogged the Reventado River, leading to massive mudflows (lahars) during the rainy season that destroyed 400 homes in Cartago. The riverbed was raised by meters, causing it to change course and threaten the Basilica of Our Lady of the Angels.

The Sector Prusia: The Walking Forest

While most tourists drive to the craters, snap a photo, and leave, the real magic of Irazú is found lower down the slopes in the Sector Prusia (Prussian Sector).

• The Reforestation Project: After the 1963 eruption destroyed much of the native vegetation, the area was replanted with exotic species to stabilize the soil. Today, you can hike through hauntingly beautiful forests of Eucalyptus (with their peeling, multi-colored bark) and Pine. The scent of pine needles in the cool mountain air makes you feel like you are in the Pacific Northwest of the USA, not the tropics.
• The Haunted Tree: One of the most photographed spots is “La Llorona” (The Weeping Woman), a massive, old tree covered in hanging moss and bromeliads that looks like a ghostly figure in the mist.
• Hiking Trails: The sector offers 16 kilometers of trails including El Roble (The Oak), Micaela, and La Gruta. These trails are popular with trail runners and families looking for a Sunday picnic spot.

The Paramo: An Island in the Sky

Visiting Irazú is not just a geological tour; it is a biological one. As you drive up the winding road from Cartago, you leave the lush tropical rainforests behind and enter a different world.

The Subalpine Paramo

Above 3,000 meters, the vegetation changes abruptly. This is the Paramo, a high-altitude ecosystem more commonly found in the Andes of Colombia and Ecuador. Irazú hosts the northernmost patch of this ecosystem in the world (along with nearby Cerro Chirripó).

• The Flora: There are no tall trees here. The landscape is dominated by dwarf shrubs, tough grasses, and lichens that can survive the freezing night temperatures and the intense UV radiation of the day.
• The “Poor Man’s Umbrella”: One of the most iconic plants is the Gunnera insignis, known locally as Sombrilla de Pobre. its massive, dinosaur-like leaves can grow up to two meters wide, providing shelter from the frequent rain.
• Myrtles and Blueberries: Look closely at the scrub, and you will find high-altitude blueberries (Vaccinium consanguineum) and dwarf myrtles, adapted to the acidic soil and thin air.

Wildlife

Despite the harsh conditions, creatures thrive here.

• Volcano Junco: Keep an eye out for this small, fearless bird with bright yellow eyes. It is endemic to the high Talamanca mountains and is often seen hopping around the crater parking lot.
• Coyotes and Armadillos: These adaptable mammals roam the scrublands near the summit.

Visiting Irazú National Park

Established in 1955, Irazú Volcano National Park is one of the most accessible volcanoes in Costa Rica. Unlike the grueling trek up Ulawun, you can drive almost all the way to the rim of Irazú.

The Experience

• Accessibility: A paved road leads right to the visitors’ center at 3,400 meters. From there, it is a short, flat walk on a sandy path to the viewing railing overlooking the main crater. This makes it one of the few places where people with limited mobility can stare directly into the throat of an active volcano.
• The Sector Prusia: For those who want to hike, the park has a second sector further down the slopes called Prusia. It features miles of trails through eerie forests of exotic pine and eucalyptus (replanted after the 1963 eruption) and native oak cloud forests.

When to Go

• The Cloud Factor: The biggest challenge is visibility. The Caribbean trade winds push moisture up the slopes, often socking the summit in thick fog by 10:00 AM.
• The Morning Rule: The golden rule for visiting Irazú is: Go early. Be at the gate when it opens at 8:00 AM. Your best chance of seeing the crater lake—and the mythical two-ocean view—is in the crisp, cold air of the early morning.

Conclusion

Irazú is a sleeping giant that watches over the heart of Costa Rica. Its history is written in the ash layers of the soil that grows the country’s famous coffee. It is a place of contrasts: fire and ice, tropical palms and alpine scrub, destruction and fertility. Whether it is glowing with a turquoise lake or shrouded in a mystical grey mist, Irazú remains the “Mountain of Thunder,” a powerful reminder of the forces that built the bridge between North and South America.