Smithsonian Institution
Bulletin of the Global Volcanism Network, v. 20, no. 11/12, November-December 1995
Arenal (Costa Rica)  Explosive activity increase from October; lava flows continue

Arenal
Costa Rica
10.463 N, 84.703 W; summit elev. 1,657 m

October plumes rose as high as 1 km above Crater C. During the
second week of November explosive activity increased, growing both
in terms of the number of outbursts and the overall quantity of
tephra emitted. Blocks and bombs landed above 1,000 m elevation.
Ash columns rose over 1 km and blew over the NW, W, and SW flanks.
Windows vibrated in buildings 6.5 km E (La Fortuna).

A lava flow first emitted in July remained mobile; one arm reached
860 m and another reached 900 m elevation. A new flow began at the
end of the month, venting from a point S of the vent for the
previous month's flow, and moving SW. Re-established vegetation in
the zone of lava flows continued to degrade due to acid rain.

For the frequency range below 3.5 Hz, there were 765 event during
October and 444 seismic events during November (figure 18). These
events chiefly occurred associated with Strombolian eruptions; some
were of sufficient amplitude to reach station JTS, 30 km from the
active crater. The largest number recorded in a single day was 40
(on 5 November). During October and November, 2.1-3.5 Hz tremor
took place for about 232 and 238 hours, respectively (figure 18).
On 15 and 17 November tremor prevailed for 21 and 20 hours,
respectively.

Information Contacts: OVSICORI-UNA (see Rincon de la Vieja).

Figure 18. Arenal seismicity and tremor for 1995 (recorded at
station "VACR," 2.7 km NE of the main crater). Courtesy of
OVSICORI-UNA.