ⓘ Arenal Volcano
Arenal Volcano is an active andesitic stratovolcano in north-western Costa Rica around 90 km northwest of San Jose, in the province of Alajuela, canton of San Carlos, and district of La Fortuna. The Arenal volcano measures at least 1.633 metres high. It is conically shaped with a crater 140 metres in diameter. Geologically, Arenal is considered a young volcano and it is estimated to be less than 7.500 years old. It is also known as "Pan de Azucar", "Canaste", "Volcan Costa Rica", "Volcan Rio Frio" or "Guatusos Peak".
The volcano was dormant for hundreds of years and exhibited a single crater at its summit, with minor fumaroles activity, covered by dense vegetation. In 1968 it erupted unexpectedly, destroying the small town of Tabacon. Due to the eruption three more craters were created on the western flanks but only one of them still exists today. Since 2010, Arenal has been dormant.
1. Geographic setting and description
Arenal is one of seven historically active Costa Rican volcanoes along with Poas, Irazu, Miravalles, Orosi, Rincon de la Vieja complex, and Turrialba. It was Costa Ricas most active volcano until 2010, and one of the ten most active volcanoes in the world. It has been studied by seismologists for many years. The volcano is located at the center of Arenal Volcano National Park in the northern zone of the country, 15 kilometres 9.3 mi southwest of the La Fortuna district in San Carlos canton, Costa Rica.
Arenal Volcano area is an important watershed for the Arenal Lake Reservoir. The reservoirs water is used for hydroelectric power. It is also connected to the national system.
Arenal has several eruptive vents. Chato is a dormant stratovolcanic cone. It is believed that Chato first erupted 38.000 years ago during the Pleistocene period and last erupted about 3.500 years ago. Chatito is a lava dome with an elevation of 1.100 metres 3.609 ft. Espina is another lava dome.
2. Geologic history
Arenal is the youngest and most active of all the volcanoes in Costa Rica. Scientists have been able to date its activity back to more than 7000 years ago. The area remained largely unexplored until 1937, when a documented expedition took place to reach the summit. It has been considered eruptive since 1968.
2.1. Geologic history July 29, 1968
On Monday, July 29, 1968, at 7:30 am, the Arenal Volcano suddenly and violently erupted. The eruptions continued unabated for several days, burying over 15 square kilometers 5.8 sq mi under rocks, lava and ash. When it was finally over, the eruptions had killed 87 people and buried 3 small villages – Tabacon, Pueblo Nuevo and San Luis – and affected more than 232 square kilometers 90 sq mi of land. Crops were spoiled, property was ruined, and large amounts of livestock were killed.
At the height of its ferocious activity, the volcano flung giant rocks – some weighing several tons – more than a kilometer half a mile away at a rate of 600 meters per second 2.000 ft/s; 1.300 mph. These explosions would go on to form three new active craters.
As the three towns were destroyed on the western side of the volcano, a town by the name of El Borio on the east side was untouched and unharmed. It is a popular myth that after the volcano ceased to erupt, El Borio was renamed La Fortuna, which means "the fortunate", referring to its luckiness that the volcano erupted to the west and not the east. However, the town was renamed La Fortuna by its residents before the 1968 eruption. La Fortuna means "The Fortune", and refers to the flat, fertile lands in the area, which are unlike the rough, mountainous terrain which surrounds most of the Arenal volcano. If the town had been renamed "The Fortunate", it would have been called "El Afortunado."
2.2. Geologic history June 1984
After a period of high effusive activity of intermittent lava flows, a new explosive phase began with 3 to 20 explosions per day of low to moderate magnitude. These explosions of steam, water, gases and ash reached altitudes of up to 5 kilometers 3.1 mi where winds again carried the material across the Arenal reservoir Lake Arenal and over the town of Tilaran.
2.3. Geologic history August 1993
A northwest wall of one of the craters collapsed and generated several pyroclastic flows. The collapsed crater wall was shaped as a V, about 60 meters 200 ft deep and 100 meters 330 ft wide. In this V-shaped crater the lava started to flow again.
2.4. Geologic history March 1994
Flows started to fill the U-shaped crater and deposited materials around the crater.
2.5. Geologic history March 1996
At this time the volcano started to produce regular lava flows, accompanied by intermittent explosions of gases. This was the regular activity of the volcano until May 5, 1998.
2.6. Geologic history May 5, 1998
The Arenal Volcano experienced a series of large eruptions on Tuesday afternoon, May 5, 1998. The first ratchet eruption was recorded at 1:05 p.m. when part of the northwest wall of the crater fell apart. Large amounts of lava, rocks, and ash flew out of the volcano during this explosion. Another eruption took place at 2:20 p.m. with material emerging from the same part of the volcano.
A specialist from the Costa Rica Volcanic and Seismic Observatory explained that the eruptions are nothing unusual for the volcano. Nevertheless, during this occasion, the amount of lava within the crater was significantly greater than normal and therefore more material was poured out. This time a landslide took place, too, as a part of the crater wall falling apart on the northwest side. This phenomenon occurs sporadically, although this time the consequences were greater than usual.
As a normal precaution, authorities declared a red alert, closed the road between La Fortuna and Tilaran, which runs around the north side of the volcano, and evacuated approximately 450 people mostly tourists from the immediate area, including several hotels and tourism-oriented businesses. There were no reports of injuries caused by the volcanic activity.
At 5:20 p.m. on Tuesday the volcano was still discharging material, but activity had decreased significantly.
2.7. Geologic history May 7, 1998
The eruptions of May 7, 1998 damaged 2 square kilometers 0.77 sq mi and destroyed a 400-by-100-meter 1.310 by 330 ft area of green forest in the vicinity of Arenal Volcano. A fissure, 500 meters 1.600 ft long and 10 meters 33 ft deep, was opened up in the wall of the crater and all the material slid down the side of the volcano.
During this day 23 eruptions were reported, between 1:05 p.m. and 7:00 p.m., and thereafter the volcano returned to its normal state. Authorities reported no unusual behavior and the national park was reopened the same week. Local seismologists investigate the activity of the volcano and park rangers continue to vigorously enforce the safety perimeter.
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