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.