Sierra Negre volcano news & eruption updates (Galapagos Islands, Ecuador)
Sierra Negra volcano (Galapagos): increased seismic activity and strong deformation, eruption warning
The Geophysical Institute of Ecuador (IG) reported last week that seismic activity now has reached levels that could be interpreted as signs of an approaching eruption. Seismic activity at the volcano has been gradually increasing over the past two years, but reached and maintained very high levels since mid May, with an average of 42 local events per day. A record number of 104 quakes occurred on 25 May. The largest-so-far quake was a magnitude 4.8 on 8 June. This and several others have been widely felt by people in the vicinity.
In addition to the dominant so-called volcano-tectonic earthquakes, which are related to internal rock fracturing due to fluid (magma) pressure creating space inside the edifice, a significant number of tremors reflecting fluid (magma, water, gas) oscillations and movements inside the volcano have also been detected.
The earthquakes have been clustering in two SW-NE trending alignments touching the NW-N rims and S-SE rims of the caldera (s. figure). Over the past weeks, most quakes have been concentrated in the eastern and southeastern segments, suggesting that this could be a likely area of new fissures opening up in the case of a new eruption.
In line with the elevated seismic activity, monitoring data shows strong ground deformation in the summit area, suggesting that a new body of magma has been intruding inside the upper volcanic edifice.
IG concludes that the recent increase of seismic activity "suggests an increase of pressure inside the volcano, which could be related to an advance of a magmatic intrusion towards relatively shallow depths", or in other words, a new eruption could be in the making although it is difficult to give a time-scale. It should be noted that the current unrest does not automatically lead to an eruption, but if it does, the most likely outcome would be a moderate-sized eruption in the Volcán Chico sector (SE).
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Lava stopped flowing at Sierra Negre volcano on the evening of 30th of Oct. 2005.
However, even 10 days after the end of the eruption, fires caused by the eruption continued, threatening some rare plants on the island. About 500 hectars in the National Park were burning on the W flank of the volcano in an area called Pampas de Velasco. This area is home to the largest population in the islands of the rare endemic plant Scalesia cordata, which was threatened by the fires. Therefore, the local authorities decided to intervene and take costly measures to extinguish the bushfire.
The eruption of Sierra Negre continues with lava flows confined to the vast caldera; it does not pose risks to populated areas. In the meanwhile, a group of scientists from the Geophysical Institute of Ecuador have visited the site and posted a detailed report about the eruption's first 3 days: it can be downloaded here.[more]
The eruption is continuing from a fissure inside the E part of the caldera of Sierra Negre, with lava fountains up to 200 m tall and large lava flows that have now covered about 20% of the caldera floor. Good eruption viewing possibilities are from a lookout on the caldera rim in the El Cura area.[more]
First photographs and more detailed information about the large eruption of Sierra Negre are emerging. As on Monday, 24 October, lava flows from a fissure have travelled 9-10 km away from the fissure. The eruption is accompanied by strong lava fountains. Near the eruption site, the terrain consists mainly of older, unvegetated lava flows. Two flows are travelling towards Elizabeth Bay, while a third one is heading towards Cartago Bay, both uninhabited areas.
The popoluation of Puerto Villamil is not threatened because of its sheltered position at the S of the island.
Sierra Negra volcano, also called "El Chico", on Isabela Island, Galapagos, erupted yesterday at 17h30 local time. As the Ecuadorian newspaper "El Universo" reports, an ash column estimated between 20 to 30 km high was observed. According witnesses from Santa Cruz island, two lava flows reached Elizabeth Bay, an uninhabitated settlement area close to the volcano. The island's main town, Puerto Villamil, 25 kilometers (15 miles) away, is not threatened by the eruption. Sierra Negro last erupted 1978.... [more]
Eruption of Sierra Negre volcano (23 Oct. 2005):
What is nearby? Near the eruption site, the terrain consists mainly of older, unvegetated lava flows. The popoluation of Puerto Villamil is not threatened becaused of its sheltered location at the S of the island. Because of the geologic characteristics (being a typical hot spot volcano, such as Hawaii), the volcanos of the Galapagos Islands produce very fluid lava flows (low viscosity) that permits the flows to travel over great distances.
Evolution of the eruption:
1) The eruption began, at 17:30 h local time on Sunday, 23 Oct. 2005, with a powerful explosion that emptied the uppermost batch of gas-charged magma, heard until 25 km away from the volcano. In addition to the noise of the explosion, a strong smell of sulphur was notised.
2) A gas and ash column rose to about 20 km above the volcano.
3) From a fissure (inferred from photographs), lava fountains started to produce lava flows observed by park rangers. Two flows are travelling towards Elizabeth Bay, while a third one is heading towards Cartago Bay. The lava flows (as on Mon. 24th of Oct.) have reached a distance of 9-10 km.
Backgound: Sierra Negre is the largest of the Galapagos volcanoes, with a caldera 10 km in diameter. Its last eruptino occurred in 1979; the lava flows of that eruption did not pose any significant risk to the population of the island.