Report on Masaya (Nicaragua) — March 2009
Bulletin of the Global Volcanism Network, vol. 34, no. 3 (March 2009)
Managing Editor: Richard Wunderman.
Masaya (Nicaragua) Phreatomagmatic explosions in August 2006; intermittent plumes through 2008
Please cite this report as:
Global Volcanism Program, 2009. Report on Masaya (Nicaragua). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 34:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200903-344100.
11.984°N, 86.161°W; summit elev. 635 m
All times are local (unless otherwise noted)
Our previous report on Masaya, in April 2006 (BGVN 31:04), summarized intermittent ash eruptions and continuing incandescence through March 2005. At that time, the visible SO2 gas emissions were the lowest seen, a condition attributed to the landslide of 2-3 March 2005 blocking the degassing vent. MODIS/MODVOLC data revealed only one pixel on 24 April 2006.
Activity during 2005-2006. The level of tremor slowly decreased from 20 RSAM units in April 2005 to 10 RSAM units a few months later. A short INETER report noted that there were no micro-earthquakes registered in October 2005. Tremor then stood at 15 RSAM (Real-time Seismic Amplitude Measurement) units, occurring with frequencies of 1.5 Hz. Gas fumes remained steady and strong. No activity was reported from April 2005 until 25-30 April 2006 when there was a small increase in emissions, with columns of gases rising ~ 100 m from the crater; there was also a strong odor of sulfur. During May, increased precipitation resulted in acid rains that burned the vegetation. In June, an observer reported a wall collapse in Santiago crater.
On the evening of 3 August 2006 seismic tremor began to increase, reaching approximately 130 RSAM units. This level was maintained throughout the next day; typically RSAM levels are at about 5 units. INETER volcanologists traveled to the volcano on 4 August and around 1030 observed two small phreatomagmatic explosions from the crater with dark gray ash. From the crater rim incandescence was seen at the bottom of the crater, and jet engine sounds could be heard. Civil Defense also reported that residents of Leon saw ash and gas emissions in the morning. Small amounts of ash fell in Cristo Rey, W of the volcano and in Las Marías to the N. Gas emissions remained strong on 4 August. Small explosions on the morning of 6 August again ejected ash. Activity decreased afterwards, with no further ash emissions and a drop in seismicity to 20 RSAM units. Minor gas emissions continued.
Overall during August 2006 the frequency of tremor shifted slightly from 1.5 to 2.0 Hz, which remained constant through August. Gas emissions increased in August 2006 at a point ~ 800 m from the cone. Gas emissions were released from the old crater as well. Temperatures at the San Fernando and Comalito cones remained unchanged. On 20 August, Martha Navarro (INETER) and Gustavo Chigna (INSIVUMEH, Guatemala), measured SO2 emissions with a COSPEC near El Crucero, (16 km W of the summit) and noted a level of ~ 900 tons of SO2 per day.
On 4 September 2006 tremor remained at 15 RSAM units, with frequencies of 1.5 Hz, a level that continued through October. Gas emissions remained constant, steady and strong. INETER reporting on 25 October 2006 discussed a new vent that opened on the floor of Santiago crater with a small lava lake. It displayed intense degassing. Following heavy rains, landslides spilled down the crater walls. Instability was noted at an overlook parking area.
Activity during 2007-2008. The Washington Volcanic Ash Advisory Center (VAAC) provided occasional reports of plumes from 26 April 2007 to 17 December 2008, predominately from GOES-12 satellite observations. Pilots and local residents also contributed observations through the VAAC and INETER.
A steam plume that drifted WSW on 26 April 2007 was visible on satellite imagery and a web camera. Additional plumes on 9 and 12 June, with little or no ash, were noted. No further plumes were reported until 24 December 2007, when a small diffuse plume, possibly containing ash, moved SW; a change in seismicity corresponded to the emission.
Pilots reported an ash plume on 29 April 2008 that was also seen in satellite imagery moving SW at 2.1 km altitude. An explosion on 18 June 2008 registered on the seismometer E of the volcano. The event discharged moderate quantities of gas and volcanic ash, and the resulting cloud was dark in color. Nearby inhabitants felt the explosion.
Satellite imagery during August 2008 revealed plumes described as steam on 12 August and gas on 18 August, both possibly containing ash. Similar plumes on 10 and 12 September drifted ENE. Pilots reported that on 9 October an ash plume rose to an altitude of 4.6 km and drifted NNE. Analysis of satellite imagery through the rest of 2008 showed possible diffuse ash and steam plumes to the SW and S on 4-5 November, a plume with possible ash on 2 December that moved SW, and a gas plume with possible ash to an altitude of 5.3-6.1 km on 17 December.
Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.
Information Contacts: Wilfried Strauch, Virginia Tenorio, and Martha Navarro, Instituto Nicaraguense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua; Jaime Cardenas Masaya Volcano National Park, Gustavo Chigna (INSIVUMEH, Guatemala); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).