Report on Fernandina (Ecuador) — 11 May-17 May 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 May-17 May 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Fernandina (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 11 May-17 May 2005. Smithsonian Institution and US Geological Survey.
0.37°S, 91.55°W; summit elev. 1476 m
All times are local (unless otherwise noted)
On 13 May the Charles Darwin Research Station (CDRS) received news that Fernandina, an island volcano in the Galapagos, had begun erupting that morning. Satellite photos showed a large cloud extending to the NW. On 14 May a joint Galápagos National Park and CDRS team flew over the eruption site. On approaching the island a large convection cloud could be seen rising above the main cloud layer above the volcano, but the caldera and rim could not be seen. On passing below the cloud, lava flows could be seen on the SW and S slopes. The first flow seems to have occurred more or less where the last eruption started in 1995, high on the SW slope, but from a circumferential fissure near the rim. The fissure itself could not be seen owing to the cloud on the rim, but map analysis suggests that the fissure was about 4.5 km long around the rim or just below it, with the first flows emanating from the W part of the fissure, and the latest flows from the E part. The flows descended the steepest part of the slopes quickly, and ponded on the gentler outer skirt of the island. The closest point that the lava had approached the sea on the 14th was 5.5 km from the coast. Lava passing through vegetated areas has caused small fires, but these have not spread far from the lava tongues themselves before going out. Most of the new flows have passed over unvegetated older lava.
A short time after the volcano started to erupt, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) flying on the OrbView-2 satellite captured an image showing a thick cloud of ash and steam fanning out W of the volcano, with a smaller, slightly darker plume blowing S. This darker plume may be more ash-rich than the larger plume, or it may be smoke from fires ignited by lava flows. Washington VAAC notices reported that the W-directed plume rose to about 5 km (17,000 feet) altitude on the afternoon of 13 May, and the S-directed plume went to 9 km (30,000 feet); both were visible later that day in satellite imagery more than 200 km from the volcano.
Thermal anomalies detected in MODIS satellite imagery, provided by the University of Hawaii, abundant on 14 and 15 May, were not evident on the 16th. Hot spots were again identified at the rim and down the S flank on 17 May.
Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.