28 September- 4 October 2005

New Activity: | Erta Ale, Ethiopia | Santa Ana, El Salvador

ERTA ALE Ethiopia; 13.60°N, 40.67°E; summit elev. 613 m

A group of scientists assessed the visible changes at Erta Ale on 26 September after activity began around 24 September. In comparison to observations made in November 2004, they found that the southern main crater/pit had widened significantly, with portions of the previous crater walls having collapsed into the lava lake. A new cone-shaped construct had grown within the southern main crater where there had been a platform. A lava lake occupied the entire width of the inner crater/pit. In the northern crater/pit, there was a solidified lava bulge and abundant "smoking" along the crater walls. No incandescent lava was visible in the pit.

Based on descriptions by local residents of seeing "red and glowing light shooting and rising into the air above the volcano," the scientists believe that a Strombolian eruption probably occurred, emitting a significant volume of fresh magma within, and possibly out of, the pit. According to news reports, about 50,000 nomads in Ethiopia's Afar region were displaced after the eruption.

Background. Erta Ale is an isolated basaltic shield volcano that is the most active volcano in Ethiopia. The broad, 50-km-wide volcano rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The 613-m-high volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located to the SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906.

Sources: Gezahegn Yirgu, Department of Earth Sciences, Addis Ababa University, Agence France-Presse

Erta Ale Information from the Global Volcanism Program

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SANTA ANA El Salvador 13.853°N, 89.630°W; summit elev. 2,365 m; All times are local (= UTC - 6 hours)

SNET reported that a sudden eruption at Santa Ana (also called Ilamatepec) on 1 October around 0820 produced an ash-and-gas plume to a height of ~10 km above the volcano (or 40,600 ft a.s.l.). According to the Washington VAAC, ash was visible on satellite imagery at a height of ~14 km (46,000 ft) a.s.l. Ash fell in towns W of the volcano, including in Naranjos, Nahuizalco, Juayúa, Ahuachapán, and La Hachadura. Volcanic blocks up to a meter in diameter fell as far as 2 km S of the volcano's crater. Lahar deposits were seen SE of the volcano. The Alert Level within a 4-km radius around the volcano's central crater was raised to Red, the highest level. According to news reports, two people were killed by landslides (possibly caused by heavy rain in the area) in the town of Palo Campana, and thousands of residents near the volcano were evacuated. As many as 1,400 hectares of crops were damaged by ash.

Prior to the eruption, significant changes in seismicity were not noted. On 3 October, after the eruption, seismicity fluctuated and small explosions occasionally occurred. Earthquakes associated with explosions were recorded. In addition, there was a decrease in the amount of sulfur dioxide emitted from the volcano. SNET noted that eruptive activity could continue at the volcano.

Background. Santa Ana, El Salvador's highest volcano, is a massive stratovolcano immediately W of Coatepeque caldera. Collapse of the volcano during the late Pleistocene or early Holocene produced a massive debris avalanche that swept into the Pacific, forming the Acajutla Peninsula. Reconstruction of the volcano rapidly filled the collapse scarp. The broad summit of the volcano is cut by several crescentic craters, and a series of parasitic vents and cones have formed along a 20-km-long fissure system that extends from near the town of Chalchuapa NNW of the volcano to the San Marcelino and Cerro Chino cinder cones on the SE flank. Historical activity, largely consisting of small-to-moderate explosive eruptions from both summit and flank vents, has been documented since the 16th century. The San Marcelino cinder cone on the SE flank produced a lava flow in 1722 that traveled 11 km to the E.

Sources: Servicio Nacional de Estudios Territoriales (SNET), Reuters, Associated Press, ReliefWeb

Santa Ana Information from the Global Volcanism Program