Arenal

July 29, 1968
After being dormant, 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 with 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 232 square kilometers 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 away at a rate of 600 meters per second. These explosions would go on to form three new active craters.

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 26 kilometers (16 mi).

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 where winds again carried the material across the Arenal reservoir (Lake Arenal) and over the town of Tilarán.

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 deep and 100 meters wide. In this V-shaped crater the lava started to flow again.

March 1994
Flows started to fill the V-shaped crater and deposited materials around the crater.

May 5th, 1998
The Arenal Volcano experienced a series of large eruptions on Tuesday afternoon, May 5, 1998. The first 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 happening is 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 (avalanche) took place, too, as a part of the crater wall fell apart on the northwest side. The 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 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 p.m. on Tuesday the volcano was still discharging material, but activity had decreased significantly

October 2010
Still, according to scientists at the National Seismological Network (RSN), Arenal is resting, not dead—a process that is natural for active volcanoes. In fact, prior to Arenal’s massive eruption of 1968, it had been inactive for some 450 years. It also entered into a resting phrase during 1973 and the early 1980s. Arenal’s inactivity – which began in October 2010 – is then simply a part of its ongoing volcanic evolution.