May – June 2015 eruption of Wolf Volcano

Initial phase of eruption. ABC News.

May 26, 2015, the Wolf volcano, Galapagos erupted for the first time in 33 years. The eruption sent a plume some 15 km into the air. It was followed by lava flows that made it all the way to the sea two days later.

Initial reports were of an ash plume moving ENE at (Flight Level) FL450 – FL500 (45,000 – 50,000 feet) from the Washington Volcanic Ash Advisory Center (VAAC). These were corroborated by seismic stations in the Galapagos recording earthquakes near Wolf. Volcano Discovery notes that the closest station was some 20 km SW of the volcano. The strongest signal was roughly 0100 and corresponded with the initial explosion from the volcano. Two hours later VAAC alerts started on a plume. By 0430 L infrared satellite sensors reported intense hot spots on the SE flank of the volcano. Visual confirmation of lava flows from the fissure eruption and lava fountains took place later in the morning on May 26.

Wolf in eruption May 26, 2015. Photo courtesy BBC. http://www.bbc.com/news/world-latin-america-32882500

The initial eruption decreased in intensity within a day. Lava fountains from the 1 km fissure had mostly stopped. The next day lava reached the ocean. Over the course of the following month, initial fissures on the flanks stopped producing lava and the action shifted to the summit caldera for the remainder of the month. There is speculation that a dike fed the initial eruption propagated from the flank fissure to the caldera. http://www.volcanodiscovery.com/wolf/activity/2015-may-25/Galapagos-Islands-eruption.html

The majority of sources have the eruption ending June2 when the flank fissures stopped flowing. Volcano Discovery writes that it continued for most of a month after its initial start. I have found nothing yet with a definitive end date or VEI number for the eruption, though I would estimate it ended up in the vicinity of a VEI 2.

Wolf in eruption May 26, 2015. Photo courtesy Telesur http://www.telesurtv.net/english/multimedia/Volcano-Wolf-Erupts-on-Isabela-Island-Galapagos-20150525-0037.html

Most of the international news about the eruption was about lava flow danger to pink iguanas and giant tortoises inhabiting the island. The animals were smart enough to get out of the way of the lava flows and there were no observed problems with their survival.

Galapagos map showing location of Wolf Volcano. http://www.slashgear.com/galapagos-islands-wolf-volcano-erupts-for-first-time-in-33-years-26385304/

Volcano

Wolf is the highest volcano of the Galapagos. It straddles the equator and tops out at some 1,710 m. The volcano erupts basalt and is a typical hot spot oceanic volcano. The volcano itself is topped by a 6 x 7 km diameter subsidence caldera, not unlike what we see on the Hawaiian Islands. The caldera is 700 m deep, making it one of the deepest on the islands. The volcano tends to erupt a higher proportion of aa lavas than other active Galapagos volcanoes.

Magma fueling Galapagos is supplied via a hot spot and neighboring spreading ridge. The Galapagos Rise was the first location that underwater hydrothermal vents and colonies of animal life were discovered. These are the black smokers, discovered first in 1977.

Satellite photo of Wolf showing new lava flows. http://www.earth-of-fire.com/page-list/actualites%20volcaniques

The volcano itself is a basaltic shield topped with a subsidence caldera. Physical lifetime above the ocean surface is similar to that of the Hawaiian Islands with the same steps of sub-aerial, aerial, post-building activity, collapse and subsidence eventually converting the original islands into seamounts. As with the Hawaiian Islands, newest islands tend to be those on the western portion of the archipelago.

Lavas from Wolf are chemically different from the lavas of neighboring Ecuador and Darwin Bay volcanoes. They are strongly similar to lavas produced on the Galapagos Spreading Center some 200 km to the north. The island itself is thought to be some 500,000 years old.

There are fewer than 1,700 people within 100 km of the volcano.

Wolf Volcano from the sea. https://commons.wikimedia.org/wiki/File:Wolf_Volcano.jpg

Eruptions

There have been at least 11 recorded eruptions from Wolf since first discovered by Europeans in 1535. The largest were VEI 2 eruptions in 1948 and 1800. Most of the material erupted via fissure eruptions. Initial portions of the eruptions tend to be quite explosive due to interaction of magma and ground water. Once the water is gone, so are the ash and steam clouds of the initial blast and the eruptions settle down to a mostly effusive model.

General tectonics of the Galapagos http://www.soest.hawaii.edu/HIGP/Faculty/hey/galapagos.html

Tectonics

The Galapagos can be traced back at least 8 Ma, with some speculation that the hot spot has been active for nearly 90 Ma. There are at least two chains of seamounts working their way eastward and northeastward from the hot spot current location. The northeast chain on the Cocos Plate, the Cocos Ridge is subducting under the North American Plate in the vicinity of Costa Rica. The eastern chain, the Carnegie Ridge is located on the Nazca Plate and is subducting under the South American Plate in the vicinity of Ecuador. There is a third truncated ridge on the Nazca Plate called the Malpelo Ridge subducting into the vicinity of the Panama – Columbia border in South America. The north and south subduction locations fuel vigorous volcanic activity across their respective front arc zones. The Malpelo Ridge does not yet appear to have made impact into the South American Plate.

Raised sea floor image of Galapagos – http://pages.uoregon.edu/drt/Research/Volcanic%20Galapagos/presentation.view@_id=9979845746990&_page=1&_part=1&.html

There is some speculation that flood basalts from the large, active hot spot may have created the Caribbean large igneous province that in turn became the Caribbean Plate some 72 – 95 Ma ago. The links are made by age and geochemical analysis of volcanic rocks. http://geology.gsapubs.org/content/30/9/795.short

Tectonic history of plate movement across Galapagos hot spot http://www.tectonicanalysis.com/site/caribbean/movie.htm

Cocos Plate movement across the hot spot is some 81 mm/yr. The slower Nazca Plate is moving some 60 mm/yr. Migration of the islands is generally westward. There is some discussion of the nature of the hot spot and the plume with the one scenario being the passage across a broad melting zone of the mantle plume. Islands are generally aligned with the westward motion of the plate across the head of the plume. The second scenario has random or episodic volcanism taking place as the plate travels across a broad hotspot anomaly. To this untrained eye, this would appear to be a distinction without a difference. Average time of travel across the plume is in the neighborhood of 5 Ma. Age of the actual plate is thought to be some 10 Ma.

Propagation of rifting and creation of Galapagos microplate over the last 2 Ma. Pacific Plate is to the left of the vertical lines on the left of the drawings. Nazca to the south and Cocos to the north. Wedge is the propagating rift system. Triangular rotating region is the newly formed Galapagos microplate. http://geology.gsapubs.org/content/36/5/339/F4.expansion.html

Given that the Galapagos are some 200 km south of the spreading center between the Cocos and Nazca Plates, one would question why there are two lines of seamounts, one on each plate. The answer is that there are active volcanoes building from the floor of the ocean north of the Galapagos Spreading Center, but the volume of magma released has not recently been sufficient to build islands like the mini hot spot some 200 km south.

Another oddity is the notion of a propagating rift system breaking away chunks of the Cocos Plate at the rate of around 50 km / Ma with an azimuth of 273 degrees away from the Galapagos hot spot. The spreading center direction changes about 8 degrees clockwise by the propagating rift. There are some 15 km of overlap along with a pattern of discrete segments. At least one paper believes it has sonar evidence of the process. http://onlinelibrary.wiley.com/doi/10.1029/JB091iB03p03369/full

NOAA Ocean Explorer: Okeanos Explorer: Galapagos Rift Expedition 2011

There is at least one paper that calls the Galapagos Rise a microplate. http://onlinelibrary.wiley.com/doi/10.1029/JB093iB11p13551/full

The spreading triple junction between the Pacific, Nazca and Cocos plate is some 1,300 km further west from the Galapagos. The Galapagos rise occupies a triangular region with one point close to the triple junction and the northern and southern legs being defined by the Cocos and Carnegie ridges.

Conclusions

Prior to the eruption, there were some observers calling Wolf an extinct volcano. Given the proximity of the archipelago to the mantle plume / hot spot and a prodigious supply of magma, that call would seem to be a bit premature.

Wolf gave us a spectacular eruption last year. My guess would be that this is not the last one we will see in the years to come, though it may be a while before the next one.

Wolf lava reaching the sea. May 29, 2015 http://thesurvivalplaceblog.com/2015/05/29/volcanoes-today-29-may-2015-sakurajima-volcano-kuchinoerabu-jima-wolf/

Additional Information

http://johngrehan.net/index.php/panbiogeography/galapagos

Plate Tectonics & Geology of the Galapagos Archipelago from Mary Jo Nehasil

http://www.mantleplumes.org/GalapagosDating.html
http://onlinelibrary.wiley.com/doi/10.1029/JB094iB10p13839/full