Report on Arenal (Costa Rica) — 5 September-11 September 2007
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 September-11 September 2007
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2007. Report on Arenal (Costa Rica). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 5 September-11 September 2007. Smithsonian Institution and US Geological Survey.
10.463°N, 84.703°W; summit elev. 1670 m
All times are local (unless otherwise noted)
In August, activity originating from Arenal's Crater C consisted of gas emissions, sporadic Strombolian eruptions, lava flows traveling down the SW and S flanks, and occasional avalanches from lava-flow fronts. Volcanic activity was at relatively low levels and few eruptions occurred. Blocks from the lava-flow fronts periodically reached vegetation and started small fires. Acid rain and small amounts of ejected pyroclastic material affected the NE and SE flanks. Eruptions produced ash plumes that rose about 2.2 km (7,100 ft) a.s.l. Pyroclastic cones on the NE and SW flanks continued to grow. Small avalanches of volcanic material traveled down several ravines. Crater D showed only fumarolic activity.
Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.