Sierra Negra

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  • Country
  • Subregion Name
  • Primary Volcano Type
  • Last Known Eruption
  • 0.83°S
  • 91.17°W

  • 1124 m
    3687 ft

  • 353050
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

26 October-1 November 2005

According to IG, an eruption began at Sierra Negra on the S end of Isabela Island on 22 October at 1730 when an explosion was heard by many people in the town of Villamil, 20 km SE of the volcano. The eruption was preceded by a seismic event on 22 October at 1438, and by earthquakes on 19 October and 2 weeks earlier. The Washington VAAC recorded an ash cloud on satellite imagery at 1745 at a height of ~15.2 km (50,000 ft) a.s.l. moving SW, and a very large hotspot. The ash cloud may have reached a height of 20 km (65,600 ft) a.s.l. Extensive lava fountains were seen rising to heights of 200-300 m along a segment of the Sierra Negra rim. Incandescent lava flowed several kilometers down the outer NW flank of the volcano's edifice and tourists reported seeing two lava flows descending the N flank. The exact orientation of flows on the volcano's flanks was not clear from early reports. Scientists did not see active lava flows in this area or evidence of flows entering the sea during an overflight on 23 October.

During a visit to Sierra Negra on 23 October, scientists saw that the eruption originated from four adjacent craters aligned along a 500-m-long fracture at the base of the inner wall of the volcano's caldera in the NE sector. Lava traveled from four principal vents southwards with exceptional force, volume, and speed downslope in several main channels. Based on observations, the main lava river traveled nearly 20 m/sec as it left its source vents. Two vents mainly supplied lava to the many lava rivers flowing southward over the northern caldera bench and then down onto the caldera floor. The feeding fracture apparently extended westward along the inner wall, but then climbed up onto the caldera rim itself where its trace was not obvious. However, small vents with fountaining and incandescent lava were observed on the rim along this general fracture system, implying that the active fracture extended for about 2 km W of the main vents.

By 23 October around 1530, the lava formed one large flow that was 1-1.5 km wide and had progressed ~7 km southeastward along the base of the eastern interior wall of the caldera, then westward along the southern wall reaching a point almost halfway across the caldera. The volume of lava ejected at this time was estimated at 25 million cubic meters. On 26 October, there were reports that lava was no longer emitted from one of the four principal vents. No populated areas on the island were threatened by the eruption.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)



 Available Weekly Reports


2005: October


26 October-1 November 2005

According to IG, an eruption began at Sierra Negra on the S end of Isabela Island on 22 October at 1730 when an explosion was heard by many people in the town of Villamil, 20 km SE of the volcano. The eruption was preceded by a seismic event on 22 October at 1438, and by earthquakes on 19 October and 2 weeks earlier. The Washington VAAC recorded an ash cloud on satellite imagery at 1745 at a height of ~15.2 km (50,000 ft) a.s.l. moving SW, and a very large hotspot. The ash cloud may have reached a height of 20 km (65,600 ft) a.s.l. Extensive lava fountains were seen rising to heights of 200-300 m along a segment of the Sierra Negra rim. Incandescent lava flowed several kilometers down the outer NW flank of the volcano's edifice and tourists reported seeing two lava flows descending the N flank. The exact orientation of flows on the volcano's flanks was not clear from early reports. Scientists did not see active lava flows in this area or evidence of flows entering the sea during an overflight on 23 October.

During a visit to Sierra Negra on 23 October, scientists saw that the eruption originated from four adjacent craters aligned along a 500-m-long fracture at the base of the inner wall of the volcano's caldera in the NE sector. Lava traveled from four principal vents southwards with exceptional force, volume, and speed downslope in several main channels. Based on observations, the main lava river traveled nearly 20 m/sec as it left its source vents. Two vents mainly supplied lava to the many lava rivers flowing southward over the northern caldera bench and then down onto the caldera floor. The feeding fracture apparently extended westward along the inner wall, but then climbed up onto the caldera rim itself where its trace was not obvious. However, small vents with fountaining and incandescent lava were observed on the rim along this general fracture system, implying that the active fracture extended for about 2 km W of the main vents.

By 23 October around 1530, the lava formed one large flow that was 1-1.5 km wide and had progressed ~7 km southeastward along the base of the eastern interior wall of the caldera, then westward along the southern wall reaching a point almost halfway across the caldera. The volume of lava ejected at this time was estimated at 25 million cubic meters. On 26 October, there were reports that lava was no longer emitted from one of the four principal vents. No populated areas on the island were threatened by the eruption.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


19 October-25 October 2005

A large eruption began at Sierra Negra on 22 October. According to the Washington VAAC, the eruption began around 1645, sending an ash cloud to ~12.8 km (42,000 ft) a.s.l. that drifted SW. A large hotspot was visible on satellite imagery. On 23 October around 0215 the cloud appeared to be at ~6.1 km (20,000 ft) a.s.l. on satellite imagery. Another eruption occurred on 23 October around 0700, and it's cloud also rose to ~12.8 km (42,000 ft) a.s.l. according to a pilot's report. By 1215, the cloud height was estimated to be at ~7.6 km (25,000 ft) a.s.l. based on satellite imagery. Although ash was no longer visible on satellite imagery on 24 October at 1215, a hotspot was seen. 25 October satellite imagery through 1315 showed the ash plume extending 220 km SW of the summit. A news article reported that three lava flows were emitted during the eruption.

Sources: Washington Volcanic Ash Advisory Center (VAAC), Associated Press


Summary of eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2005 Oct 22 2005 Oct 30 Confirmed 3 Historical Observations North caldera rim
1979 Nov 13 1980 Jan 14 (in or after) Confirmed 3 Historical Observations Upper NW and NE flanks (Volcán Chico)
1963 Apr 13 1963 May Confirmed 2 Historical Observations Volcán Chico area & NW caldera rim
1957 Unknown Confirmed   Unknown
1954 Nov 9 Unknown Confirmed 2 Unknown Upper NNE flank
1953 Aug 27 1954 Jan Confirmed 3 Historical Observations Volcán Chico area & NW caldera rim
1948 Aug 1949 Feb (?) Confirmed 2 Historical Observations
1911 Dec 31 ± 365 days Unknown Confirmed   Historical Observations
1860 Unknown Confirmed 2 Unknown
1844 Unknown Confirmed 0 Unknown
1817 Unknown Confirmed   Unknown
1813 Jul 13 Unknown Confirmed 2 Unknown
1350 ± 500 years Unknown Confirmed 0 Surface Exposure
1060 ± 500 years Unknown Confirmed 0 Surface Exposure
0370 ± 1000 years Unknown Confirmed 0 Surface Exposure
1250 BCE ± 100 years Unknown Confirmed 0 Radiocarbon (uncorrected) SE flank
8250 BCE ± 1000 years Unknown Confirmed 0 Surface Exposure

The following references are the sources used for data regarding this volcano. References are linked directly to our volcano data file. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title. Additional discussion of data sources can be found under Volcano Data Criteria.

Delaney J R, Colony W E, Gerlach T M, Nordlie B E, 1973. Geology of the Volcan Chico area on Sierra Negra volcano, Galapagos Islands. Geol Soc Amer Bull, 84: 2455-2470.

Geist D J, Harpp K S, Naumann T R, Poland M, Chadwick W W, Hall M, Rader E, 2008. The 2005 eruption of Sierra Negra volcano, Galapagos, Ecuador. Bull Volc, 70: 655-673.

Geist D, Harpp K, Reynolds B, 2006. A field trip guide to the geology of the Galapagos Islands. Cities on Volcanoes 4, Quito, Ecuador, 23-27 Jan, 2006, Field Trip Guide, 30 p.

Goff F, McMurtry G M, Counce D, Simac J A, Roldan-Manzo A R, Hilton D R, 2000. Contrasting hydrothermal activity at Sierra Negra and Alcedo volcanoes Galapagos Archipelago, Ecuador. Bull Volc, 62: 34-52.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Jonnsson S, Zebker H, Amelung F, 2005. On trapdoor faulting at Sierra Negra volcano, Galapagos. J Volc Geotherm Res, 144: 59-71.

McBirney A R, Williams H, 1969. Geology and petrology of the Galapagos Islands. Geol Soc Amer Mem, 118: 1-197.

Mouginis-Mark P J, Rowland S K, Garbeil H, 1996. Slopes of western Galapagos volcanoes from airborne interferometric radar. Geophys Res Lett, 23: 3767-3770.

Naumann T, Geist D, 2000. Physical volcanology and structural development of Cerro Azul volcano, Isabela Island, Galapagos: implications for the development of Galapagos-type shield volcanoes.. Bull Volc, 61: 497-514.

Reynolds R W, Geist D, Kurz M D, 1995. Physical volcanology and structural development of Sierra Negra volcano, Isabela Island, Galapagos Archipelago. Geol Soc Amer Bull, 107: 1398-1410.

Richards A F, 1962. Archipelago de Colon, Isla San Felix and Islas Juan Fernandez. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 14: 1-50.

The broad shield volcano of Sierra Negra at the southern end of Isabela Island contains a shallow 7 x 10.5 km caldera that is the largest in the Galápagos Islands. Flank vents abound, including cinder cones and spatter cones concentrated along an ENE-trending rift system and tuff cones along the coast and forming offshore islands. The 1124-m-high volcano is elongated in a NE direction. Although Sierra Negra is the largest of the five major Isabela volcanoes, it has the flattest slopes, averaging less than 5 degrees and diminishing to 2 degrees near the coast. A sinuous 14-km-long, N-S-trending ridge occupies the west part of the caldera floor, which lies only about 100 m below its rim. Volcán de Azufre, the largest fumarolic area in the Galápagos Islands, lies within a graben between this ridge and the west caldera wall. Lava flows from a major eruption in 1979 extend all the way to the north coast from circumferential fissure vents on the upper northern flank. Sierra Negra, along with Cerro Azul and Volcán Wolf, is one of the most active of Isabela Island volcanoes.