Report on Concepcion (Nicaragua) — 27 July-2 August 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 July-2 August 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Concepcion (Nicaragua). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 27 July-2 August 2005. Smithsonian Institution and US Geological Survey.
11.538°N, 85.622°W; summit elev. 1700 m
All times are local (unless otherwise noted)
According to INETER, an eruption occurred at Concepción on the island of Ometepe on 28 July at dawn. Ash fell in the town of Moyagalpa (W of Ometepe island), and in the zones of Rivas, San Jorge, Buenos Aires, Potosí, and Belén. Seismic tremor was recorded at a seismic station N of the volcano, but no large earthquakes were recorded. By the afternoon, ashfall had reduced considerably or completely ceased, while gas emission continued. No thermal anomalies were observed on satellite imagery. On 29 July during 0500-0800, a series of volcanic earthquakes occurred that may have been associated with small explosions in the crater. At 1025 the seismic station recorded a moderate explosion in the crater. On 31 July, seismic tremor occurred with slight variations. According to news articles, no one was injured by the eruptions.
Geologic Background. Volcán Concepción is one of Nicaragua's highest and most active volcanoes. The symmetrical basaltic-to-dacitic stratovolcano forms the NW half of the dumbbell-shaped island of Ometepe in Lake Nicaragua and is connected to neighboring Madera volcano by a narrow isthmus. A steep-walled summit crater is 250 m deep and has a higher western rim. N-S-trending fractures on the flanks have produced chains of spatter cones, cinder cones, lava domes, and maars located on the NW, NE, SE, and southern sides extending in some cases down to Lake Nicaragua. Concepción was constructed above a basement of lake sediments, and the modern cone grew above a largely buried caldera, a small remnant of which forms a break in slope about halfway up the N flank. Frequent explosive eruptions during the past half century have increased the height of the summit significantly above that shown on current topographic maps and have kept the upper part of the volcano unvegetated.