Small explosions have been recorded at Nicaragua's Telica volcano regularly since early in the 20th century. The last major eruptive episode began with a series of small explosions in March 2011 and culminated in greatly increased seismicity and several larger explosions during May that deposited ashfall in communities within 8 km of the volcano, and caused a small number of evacuations. Ash-bearing explosive activity died down by mid-June 2011, although steady degassing with gas-and-steam plumes continued. A small ash-and-gas explosion was reported on 25 September 2013.

On 7 May 2015 a new series of larger ash-and-gas explosions began. Nicaragua's Instituto Nicaragüense de Estudios Territoriales (INETER) provides monthly reports on seismic activity and monitoring of thermal and geochemical data as well as daily informational bulletins of volcanic activity; aviation advisories are also provided by the Washington Volcanic Ash Advisory Center (VAAC). Activity from June 2014 through August of 2016 is covered in this report.

A decrease in seismicity and increase in temperature within the summit crater at Telica in April 2015 preceded an ash-and-gas explosion on 7 May 2015 after several years of relative quiet. This was followed by a series of over 100 ash-bearing explosions in the following three weeks, the last on 28 May. Degassing from fumaroles continued without ash during June and the crater had cooled significantly by August. A new series of ash-and-gas explosion between 23 and 26 September 2015 sent ashfall to nearby communities and a few large volcanic bombs several hundred meters from the crater. The next series of explosions between 22 and 29 November sent ashfall to over 70 communities within 20 km of Telica. Incandescence was observed in a crack in the floor of the summit crater in December, but lava wasn't observed in the vent until 25 February 2016 after a sequence of gas explosions that lasted until 1 March. The lava and incandescence were observed until early May when explosions on 7-8 May 2016 were observed from a new vent in the N part of the crater. No further ash emissions were observed, and seismicity dropped significantly and remained quiet through August 2016.

Activity between June 2014 and May 2015. Remote temperature measurements of the summit crater floor at Telica showed a steady decline between May and July 2014 from an average of 417°C to 350°C, continuing a decline from values measured in 2013 that had been as much as 100°C hotter. During this time, few noises were heard and little incandescence from the crater was observed. There were no further reports until February 2015 when fresh landslides along the SE inner wall were observed blocking the vent; on a 25 February summit crater visit there was no noise, and few emissions from fumaroles were observed. Temperatures at the fumaroles on the SE, S and SW walls of the crater were around 150°C, and the floor of the crater was measured at 123°C with the Testo IR 820 thermometer. Gas emissions were more variable in March 2015, but again there was no noise or incandescence observed. The numbers of daily seismic events in March 2015, 3982, were generally within normal levels, ranging from a few to a few hundred per day, depending on type of seismicity.

The temperature at the floor of the crater in April 2015 had risen significantly to 412°C. The seismicity was also changed, with fewer total events (1,973). There was a noticeable drop in the number of events in the second half of April. As reported by INETER seismologist Virginia Tenorio, this decrease in number of events, accompanied by a narrowing of the frequency range to between 3 and 11 Hz, from a normally larger range of 3 to 30 Hz, also occurred prior to the last significant eruption in 2011.

Activity during May-August 2015. On 7 May 2015 at 1609 and 1615, INETER reported that Telica broke its "relative calm" since 26 September 2013 with two gas and ash explosions which rose about 200 m above the rim of the crater. This was the beginning of an eruptive period that included 902 seismically-detected explosions between 7 and 28 May, of which 104 were accompanied by volcanic ash (figure 35). Some also involved ejection of large incandescent lava blocks. Towns within 40 km in a generally W direction were affected by ashfall from these explosions.

Figure 35. Number of explosions per day at Telica during 7-31 May 2015. Top: Total explosions. Bottom: Explosions with ash. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

An explosion on 12 May ejected rocks 400 m high to the W. Minor ashfall was reported during May in El Realejo (35 km WSW), Corinto (40 km WSW), Posoltega (16 km SW), Guanacastal (20 km WSW), Quezalguaque (12 km SW), Chinandega (30 km W), El Viejo (35 km WNW), and Chichigalpa (20 km WSW). On 20 and 21 May, a series of explosions ejected one-m-diameter blocks up to 500 m from the crater. Many ash plumes were photographed by the INETER web camera located at the TELN seismic station on the E flank; others by INETER scientists at the volcano (figures 36-40).

Figure 36. Explosion at Telica on 8 May 2015 at 1002 local time. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

Figure 37. Explosion at Telica photographed by the web camera at seismic station TELN on the E flank, 17 May 2015, 0957 local time. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

Figure 38. Incandescent ejecta from Telica at 1906 local time on 20 May 2015. Photographed by the web camera at the TELN seismic station on the E flank. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

Figure 39. Block ejected from Telica on 23 May 2015. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

Figure 40. Ash explosion at Telica, 1000 local time 27 May 2015. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

On only two dates during May did these explosions initiate reports from the Washington VAAC; they reported ash emissions on 11 May rising to 1.8 km and drifting W, and twice on 26 May. The first plume on 26 May extended 75 km W below 3 km altitude, and a second drifted 117 km WNW of the summit at 4.3 km before dissipating.

Visits to the crater on 8 and 14 May revealed a new vent at the base of the S wall of the crater that formed during the 7 May explosion (figure 41). There was a substantial increase in temperature inside the crater from 150°C to 377°C between these dates. The first explosion with incandescent material was observed on 10 May. SO₂ measurements of 1,000-1,500 tons per day (t/d) were taken during an explosion on 26 May (figure 42), and values were significantly higher than previous levels of around 300 t/d.

Figure 41. New vent on the S wall of the summit crater at Telica formed during the 7 May explosion. Photo taken 8 May 2015. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

Figure 42. Ash explosion at Telica, 26 May 2015 during which SO2 measurements of 1,000-1,500 tons per day (t/d) were measured. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Mayo 2015).

Seismicity in May was high, with 18,858 recorded events. The high number of volcano-tectonic events (VT) during the month (605) was associated with the ruptures that triggered explosions; they have a characteristic frequency of 4.5 to 10.0 Hz. Most of the VT events were located between 6 and 10 km below the surface. The majority of the total seismic events in May were related to degassing and gas explosions (18,087). Screw-type "tornillo" earthquakes are usually rare at Telica, but about 46 of them were observed in May.

The volcano remained relatively calm during June, with the number of daily seismic events typically at 10 or lower, far fewer than May. Even fewer seismic events (71) were recorded in July along with gas emissions that were variable but generally light. The most degassing came from fumaroles located on the inner walls of the crater where the temperature was measured at 298°C. On a 25 August visit to the crater, INETER technicians noted that the points where incandescence had been observed prior to May had disappeared, and temperatures at the fumaroles on the SW and NE walls ranged from 50°C to 160°C.

Activity during September 2015-August 2016. A new gas-and-ash explosion at 0800 on 23 September 2015 sent ash to the NW, W, and SW. The plume rose to 400 m above the crater. Other smaller explosions with small quantities of ash continued that day and the next. Ashfall was reported in the community of Guanacastal (20 km WSW). Additional medium-intensity explosions on 26 September ejected gas, ash, and rock fragments up to 500 m from the crater. Ash plumes reached 1,000 m above the crater and drifted W and NW. The Washington VAAC reported these emissions at 4.3 km altitude, drifting N and W about 45 km (figure 43). This second series of explosions opened a new vent on the N side of the crater floor, and gas emissions continued from both vents. Seismic events in September numbered 775.

Figure 43. Ash explosion at Telica at 0845 (local time) on 26 September 2015. Location uncertain but likely in the vicinity of Leon, about 20 km S of the volcano. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Septiembre 2015).

During October, no ash explosions were recorded, although 2,921 total seismic events were reported. On 22 November 2015 a new series of explosions began, lasting for eight days. That day, the Washington VAAC reported an ash plume to 2.4 km that drifted about 185 km W. According to a news article published by el19, two explosions, at 0847 and 0848, generated ash plumes that rose 2 km and ejected tephra at least 900 m away (figure 44). Residents in Agua Fría (900 m away) noted it was the first time lapilli and blocks had reached their community. La Prensa reported that ash fell in at least 70 communities in the municipalities of Quezalguaque (13 km SW), Posoltega (16 km WSW), Chichigalpa (20 km WSW), and Chinandega (30 km W).

Figure 44. Explosion at Telica at 0845 (local time) on 22 November 2015. Taken from the web camera at seismic station TELN on the E flank. Courtesy of el19 digital.com (https://www.el19digital.com/articulos/ver/titulo:35988-volcan-telica-registra-fuerte-explosion ).

INETER reported that during 25-27 November numerous small explosions were recorded, most of which generated volcanic ash, with the highest plume reaching 800 m above the crater. Satellite imagery reported from the Washington VAAC showed a faint plume extending about 16 km WSW at 1.2 km altitude on 26 November. Occasional emissions continued until 29 November with several VAAC reports indicating plumes at 1.5 km altitude visible in satellite imagery drifting up to 45 km W and SW.

While no explosions were reported during December 2015, the INETER volcano observer (René Dávila) noted that incandescence was observed in a N-S trending fracture on the crater floor during a visit to the summit. Seismicity was low in December, with a total of 1,342 events recorded, although there was an increase in micro-seismicity during the second half of the month. Even fewer seismic events were reported in January 2016 (171 events), along with few gas emissions that seldom rose above the crater rim.

On 13 February 2016 emissions were observed in visible satellite imagery by the Washington VAAC moving WSW from the summit that likely contained ash. This was preceded by a burst of seismic activity reported by INETER. They noted intermittent high micro-seismicity between 16 February and 1 March. Incandescence from the vent on the crater floor increased during February; lava on the crater floor was first observed by INETER on 25 February. Small gas explosions were observed inside the crater during 24- 26 February followed by five gas-and-ash explosions recorded during 29 February-1 March which generated plumes that rose 300 m above the crater and drifted W and SW. Gas-and-ash emissions lasted for 14 minutes during the strongest of these events.

A visit to the crater on 15 March 2016 by INETER scientists provided additional evidence of incandescence within the crater and a temperature reading of 485° C (figure 45).

Figure 45. Night view of the incandescence in the crater of Telica taken on 15 March 2016. Courtesy INETER (Boletin mensual Sismos Y Volcanes de Nicaragua, Marzo 2016).

From late March through early May, INETER reported incandescence and lava inside a vent on the crater floor, and micro-seismicity remained high even though gas emissions and RSAM values were low. The last report of incandescence from the vent on the crater floor was during the second week of May. RSAM values had dropped to 80 units by 14 May.

Based on information from INETER, SINAPRED reported that 30 explosions occurred during 7-8 May 2016, producing gas-and-ash plumes that rose 600 m and drifted S and SW. The explosions originated from a new vent in the N part of the crater. Seismic RSAM amplitudes spiked to several hundred units between 8 and 12 June, but there were no reports of ash emissions after 8 May from either the Washington VAAC or INETER.

In late July 2016 scientists visited the Las Quemadas, Aguas Frías, (Hot Spring) located 1.7 km north-east of Telica to study temperature and chemistry of the geothermal waters. Seismicity and RSAM values remained low through August 2016 with no further reports of ash emissions or lava in the crater.

Geological Summary. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/ , archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Sistema Nacional para la Prevencion, Mitigacion y Atencion de Desastres, (SINAPRED), Edificio SINAPRED, Rotonda Comandante Hugo Chávez 50 metros al Norte, frente a la Avenida Bolívar, Managua, Nicaragua (URL: http://www.sinapred.gob.ni/); El19digital, https://www.el19digital.com/articulos/ver/titulo:35988-volcan-telica-registra-fuerte-explosion; La Prensa, http://www.laprensa.com.ni/2015/11/22/departamentales/1940877-volcan-telica-lanza-piedras-cenizas-dos-mil-metros-altura .