Irazu - Part 2

Irazu - the Colossus.


Irazu, towering over the valley, as seen from the city of Cartago


Another view of Irazu from the Central Valley.


Farmland seen on the drive up.


Onion fields on the slope above the Central Valley.



Looking toward the east about half way to the summit.


A field on the up slope side of the highway about half way to the summit.


A view of the summit.


Fields ready for planting.



Potato fields just below the frost line.


Irazu Volcano is a stratovolcano with an irregular subconic shape. It is located in the Cordillera Central near the city of Cartago. There’s some disagreement about the source of the volcano’s name. There are three possible sources. One: it is thought by some to be a corruption of the word Iztaru which was the name of a village of indigenous peoples on the volcano’s slopes. Two: That it came from the word Istaru which means thunder and earthquake mountain. And three: That it is a word formed from two words - Ara which means point and Tzu which means thunder. Aratzu = point of thunder.

Irazu is known as the “Colossus” because of its past catastrophic eruptions and its size. It has erupted frequently in the past - 23 times since records began to be kept concerning its activity back in 1723 by Diego de la Haya. It is the highest volcano in Costa Rica, reaching an altitude of 11,259 feet above sea level. And it is the largest, covering 200 square miles.


Irazu’s summit is made up of five craters:
Main Crater
Diego de la Haya
Playa Hermosa
La Laguna
El Piroclastico


All five craters can be seen in this aerial photo.


The main crater is in the foreground. Diego de la Haya is to the left. Playa Hermosa is to the right.


The main crater (El Crater Principal) is 3445 feet across and 984 feet deep. It contains a lake that is green in color. This lake has been known to change from its normally green color to red from time to time. This is due to a change in its chemical make-up. The government’s geological agency keeps a close watch on Irazu just as it does all the active volcanoes in the country. They closely monitor the lake for any changes in temperature or chemical make-up. I have never personally seen this.

The main crater is in the foreground. Diego de la Haya is to the left. Playa Hermosa is to the right.

Diego de la Haya is an old crater that is no longer active. It was named after de la Haya who was the first to record an eruption (1723). It does at times have a small lake that is formed by the run-off water during the rainy season.

Playa Hermosa from near the rim of the main crater.

Playa Hermosa (which means beautiful beach) is also an old, inactive crater. When you stroll along there you are actually walking on the plugged vent. The surface is a fine sand of black glass. Very abrasive. There are various sizes of black pumice scattered across the surface. Nature is reclaiming Playa Hermosa. Hardy grasses and small flowers are beginning to grow there.

Playa Hermosa from the slope above the main crater.

The main crater from the summit.

The Central Valley shrouded in clouds. Viewed from the summit.



La Laguna (the lagoon) and El Piroclastico (piroclastic) are also old craters. Both are inactive.

The last major eruption was in 1963 - 1965, during which time the Costa Rican captial, San Jose, and the Central Valley were blanketed daily in black soot, ash, and sludge for months. At one point during this period of activity ash-filled vapor blasted up into overhanging clouds, triggering a storm that rained mud over a wide area. The accumulation of mud was up to five inches thick.

The last actual eruption was in December of 1994 and was considered a phreatic eruption. Basically, the volcano hiccupped gas, breccia, and ash. Presently, local geologists consider Irazu to be dormant. There are, however, frequent earthquakes which indicates that magma is still moving beneath the volcano. Presently, Irazu is behaving. There is little activity beyond the release of occasional clouds of carbon dioxide gas and hydrogen gas at temperatures below the boiling point of water.

At 11,259 feet above sea level, Irazu is often quite frigid at the top. The summit is above the frost line. Temperatures are sometimes around freezing. An average temperature is 45 degrees F. The low temperature, combined with the ceaseless wind and the saturating humidity, make it bitter cold at the rim. This is quite a surprise to people who come in summer clothing thinking they are in a tropical climate because Costa Rica is so near the equator. I have personally been at the rim when it was sleeting!

In order to see the craters, it is best to arrive early in the morning before the clouds move in. However, a cloudy valley does not mean Irazu’s summit won’t be clear. Because of the volcano’s altitude it is often above the clouds.

The landscape is surreal. Lunar-like and grey. Harsh. Desolate. The plant growth is stunted and there is little in the way of wildlife beyond birds, rabbits, coyotes, and armadillos.
Caution is required. The crater rims are dangerously unstable.

I have been to Irazu many times. It is hushed and eerie, especially when the clouds roll in. There are days when there are very few people and then there are days, especially when the sun is out, that there are too many. Many people seem to have no idea of how to conduct themselves in such a harsh environment or to understand that they are at 11,259 feet above sea level. On one of my visits to Irazu a middle aged man in a spandex suit of some sort (it was sort of a neon green in color - scarey) decided that Playa Hermosa was a great place to run. He took off at a dead run, and passed out after the first 50 feet or so. Apparently he did not realize that the air is quite abit thinner at 11, 259 feet than it is at sea level.

Hope you enjoyed our journey to Irazu. The next volcano we will visit will be Poas.

Blessings!