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The activity of Arenal Volcano
Estimated to be less than 3,000 years old, Arenal is a
geologically young volcano. During the various cycles of its
life activity has been characterized by an alternating of an
explosive, effusive phase with one of weak, explosive activity.
Major events in recent history begin with the 1968 killer
AM "Cerro" Arenal--as it was called by local residents--began
explosive activity that literally blew the west side off the
volcano. Two villages at the foot of the volcano-- Pueblo Nuevo
and Tabacón--were completely destroyed and 78 people died.
Between July 29 and 31 three new craters were formed on the
western flank of the volcano and a fifteen-square kilometer area
(5.8 square miles) was devastated.
this month a period of explosive activity resulted in four
strong explosions that blew large amounts of ash into the sky.
The ash was carried as far away as Tilarán, 26 kilometers (16
miles) distant. There were also several burning avalanches
originating in the top crater that were channeled by the valley
of the Tabacón River on the northwestern flank of the volcano.
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.
month saw expulsions of pyroclastic flows (ash and rock of no
more than one centimeter that appear when the rock breaks
apart). Some 500 of the larger, one-centimeter size fell near
the thermal pools of Tabacón Resort.
this month the volcano has produced regular lava flows,
accompanied by intermittent explosions of gases. Until May 5,
1998 this was the regular activity of the volcano.
information is based on reports in the Costa Rica daily La
Nación after the Tuesday eruption) Arenal Volcano experienced a
series of large eruptions on Tuesday afternoon, May 5, 1998. The
first was recorded at 1:05 PM local time (US Central Standard
Time). In that explosion. part of the northwest wall of the
crater fell away. Large amounts of lava, rock and ash issued
from the volcano in this explosion. Another eruption took place
at 2:20 PM local time with material falling from the same area
of the volcano.
specialist with the Costa Rica Volcanic and Seismic Observatory
explained that what occurred Tuesday is relatively frequent with
this volcano. On this occasion the amount of lava within the
crater was great and therefore more material left the crater.
Also, this time there was a landslide (avalanche) as part of the
crater wall fell away on the northwest side. This volcano
produces similar phenomena periodically, although this time it
was much larger than usual.
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 which includes several
hotels and tourism oriented businesses. There were no reports of
injuries from the volcanic activity.
PM on Tuesday the volcano was still discharging material, but
activity had decreased significantly.
Tuesday's eruptions damaged two square kilometers and burned a
400 by 100- meter area of green forest on the side of Arenal. A
fissure in the wall of the crater 500 meters long by 10 meters
deep was also opened up. All this material slid down the side of
the volcano. Experts say there is currently a risk of avalanches
of this loose, accumulated material, especially when the heavy
Tuesday's episode there were a total of 23 eruptions between
1:05 PM and 7 PM local time, after which the volcano returned to
its normal state. During this time there were only two major
eruptions of gases.
area around Arenal Volcano is a high-risk zone--this volcano has
been active for the past 30 years with regular eruptions
providing tourists excellent displays of nature's awesome power.
The volcano has become an important tourist attraction for Costa
Rica. Several hotels, restaurants and other tourist-oriented
ventures have sprung up very close to Arenal in recent years.
Referring to this explosion of tourism infrastructure,
volcanologist Jorge Barquero of the Costa Rica Volcanic and
Seismic Observatory stated that Arenal's activity on Tuesday is
normal in an active volcano like this one, but what is not
normal is that man has developed construction in such a
high-risk zone. Barquero also commented that in this incident
the volcano was telling us that just like this eruption, there
could be others of greater magnitude at any moment, possibly
with regrettable consequences.
May 31 addendum
the eruption of May 5, Arenal returned to its typical occasional
rumblings. Authorities reported no unusual behavior and the
national park was reopened the same week. Local volcanologists
continue to keep a close watch on the volcano and park rangers
continue to vigorously enforce the safety perimeter.