Editing Arenal Volcano (section)

==Geologic history==
Arenal is the youngest of all the volcanoes in Costa Rica. Scientists have been able to date its activity back more than 7000&nbsp;years. The area remained largely unexplored until 1937, when a documented expedition took place to reach the summit.<ref>{{cite web|url=http://www.CostaRica21.com/Arenal-Volcano.html#Facts_&_Data |title=Arenal Volcano, Costa Rica. Recent Eruption & Activity 2012, 2010 |publisher=Costarica21.com |access-date=2015-06-19}}</ref> It was eruptive from 1968 until 2010.<ref name="GVP"/>

===July 29, 1968===
[[File:CostaRica Arenal Volcano 1968Flow (pixinn.net).jpg|thumb|left|Arenal in 2014, viewed from the old 1968 lava flow.]]
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 {{Convert|15|km2||abbr=|sp=us}} under rocks, lava and ash. When it was finally over, the eruptions had killed 87 people and buried 3 small villages – Tabacón, Pueblo Nuevo and San Luís – and affected more than {{Convert|232|km2||abbr=|sp=us}} of land. Crops were spoiled, property was ruined, and large numbers of livestock were killed.<ref>{{cite web|url=http://www.arenal.net/arenal-volcano-1968-eruption.htm |title=Arenal Volcano 1968 eruption |publisher=Arenal.net |access-date=2015-06-19}}</ref>

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 {{Convert|600|m/s|ft/s mph|abbr=|sp=us}}.<ref>{{cite web |last1=Alvarado Induni |first1=Guillermo |title=El devastador despertar del volcán Arenal en 1968 |url=https://www.nacion.com/ancora/el-devastador-despertar-del-volcan-arenal-en-1968/EG5QBTRSLVDEJBRE3GIGZWJHXQ/story/ |website=nacion.com |date=July 28, 2018 |publisher=La Nación |access-date=18 January 2023}}</ref> 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 Fortune", 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. "The Fortune" refers to the flat, fertile lands in the area, which are unlike the rough, mountainous terrain which surrounds most of the Arenal volcano.

===June 1975===
Between the 17th and the 21st of June 1975 several avalanches went down from one of the craters. The vegetation along Tabacon River was destroyed and a great amount of material was deposited on the riverbed. Four strong explosions also blew large amounts of ash into the sky. The ash was spread within a distance of {{convert|26|km|mi|sp=us}}.

===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.

===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&nbsp;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&nbsp;p.m. with material emerging from the same part of the volcano.

A specialist from the Volcanological and Seismological Observatory of Costa Rica (OVISCORI) at the [[National University of Costa Rica]] 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 [[volcanic landslide|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, San Carlos|La Fortuna]] and [[Tilarán]], 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&nbsp;p.m. on Tuesday the volcano was still discharging material, but activity had decreased significantly.

===May 7, 1998===
The eruptions of May 7, 1998 damaged {{Convert|2|km2||abbr=|sp=us}} and destroyed a {{Convert|400 by 100|m||abbr=|sp=us|adj=on}} area of green forest in the vicinity of Arenal Volcano. A fissure, {{Convert|500|m||abbr=|sp=us}} long and {{Convert|10|m||abbr=|sp=us}} 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&nbsp;p.m. and 7:00&nbsp;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 [[Seismology|seismologists]] investigated the activity of the volcano and park rangers continued to vigorously enforce the safety perimeter.

===October 2010===
October 2010 was the last eruption reported, and the presence of [[fumerole]]s were reported at the summit. Arenal was placed under Green Alert (calm status) by local authorities.

=== September 2013 ===
In September 2013, Arenal Volcano displayed signs of activity following a period of dormancy. On September 8 and 9, plumes composed primarily of water vapor were observed rising from the northeastern and southeastern edges of Crater C. Additionally, tremors associated with hydrothermal and magmatic activity were recorded on September 8. In the following weeks, an increase in rockfalls and rumbling noises was documented. While no eruption occurred, these observations indicated ongoing geothermal processes within the volcano.<ref>{{Cite web |title=Arenal volcano, Costa Rica: news & activity updates |url=https://www.volcanodiscovery.com/arenal/news.html |access-date=2025-03-10 |website=www.volcanodiscovery.com |language=en}}</ref>