After a three year quiet period, in July 2013 a pilot-reported ash plume rising to an altitude of 18,000 ft a.s.l. signalled the start of a three month eruptive phase at Ubinas. GVP reported that this eruptive activity was VEI 2 . Ubinas has been restless again since January 2014, following resumption of seismic activity, with frequent plumes of gas and usually light ash. By 14 April 2014 she was producing explosive eruptions with ash plumes up to 37,000 ft a.s.l. [1,2].
The current alert level was raised to orange on 16 April 2014, following a significant increase in the exhalation energy values / explosions, suggesting a possible breaking of the dome. SO2 levels indicate that magma is continuing to rise. The eruption of pyroclastic fragments of 20 cm to 30 cm to a distance of 1.5km to the west of the crater was reported on 15 April 2014. 
Evacuations of people and livestock from Moquegua and Arequipa to temporary shelters have commenced as a precautionary measure. An eruption on 2006 released toxic gasses and ash which killed livestock . Jose Machare from the Peruvian Institute of Geophysics is quoted as saying that there was a “low possibility” that that latest activity could develop into an “unusual eruption that could be very big”. 
Geology of Ubinas
Ubinas is one of Peru’s most active volcanoes, comprised of layers of silica-rich lava flows. At the summit there is a 1.4 km wide and 150 m deep caldera which contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. [1,11]
She is situated about 50 km behind the main volcanic front of Peru, 230 km east of the Peru-Chile trench in the Central Volcanic Zone on a plateau formed from Oligocene-Miocene (Neogene) ignimbrites and intrusive rocks. Here, the Nasca plate subducts beneath the South American plate at a dip of 20° -30°. Ubinas, herself, is about 150km above the Benioff-Wadati plane. [5,6]
Plotting the latest 3,000 earthquakes reported by IRIS for the area shown below, we can see the subduction zone:
Latitude v Longitude as shown by IRIS:
Ubinas’ lavas range from mafic to rhyolitic. She has produced at least two Plinian deposits – the most recent of which occurred between 1000AD and 1160AD, comprising a thick layer of andesitic pumice which was more than 25 cm deep 40 km from the summit. [1,5,6]. Her lavas are sourced from 1) hydration melting (partial melting of the mantle caused by dehydration of the descending slab); and, 2) the mixing of lavas in the feeding magma reservoir. Basaltic magmas from the mantle mix with magmas generated at the base of the crust and in a thickened continental crust .
Ubinas developed in two phases: the first phase, Ubinas I, is more than 376,000 years old; and, the second phase, Ubinas II, dates from the mid-Pleistocene. [5,6]
Ubinas I is a low lying volcano with andesite and dacite lava flows. Her SE flank collapsed about 3,700 years ago resulting in debris avalanche flows that extend 12km downstream of the Rio Ubinas. Subsequent eruptions deposited non-welded ignimbrites and pumice deposits. [5,6]
Ubinas II is an andesitic-to-rhyolitic stratovolcano with a summit elevation of 5,672 meters. The caldera at the summit was formed less than 20,000 years ago from Plinian activity. The inner crater is under 200 m high and shows extensive hydrothermal alteration and fractures. Frequent explosive eruptions from the inner crater over the last 10,000 years have led Thouret et al. to suggest that the caldera may be gravitationally unstable. [5,6,7]
Eruptive activity has been documented from 1550. Her most recent eruptions have been moderate explosive eruptions . However, in the light of her history, there is a risk of a something larger.
Hope you enjoyed reading this. The usual caveats apply: “not an expert, etc …”
KarenZ, April 2014
- GVP: http://www.volcano.si.edu/volcano.cfm?vn=354020#July2013
- Buenos Aires VAAC: http://www.smn.gov.ar/vaac/buenosaires/productos.php
- “Residents evacuated from homes as Peru volcano spews ash”, 18 April 2014,http://www.bbc.co.uk/news/world-latin-america-27078279
- “Peru Evacuates 28,000 Llamas, Alpacas From Active Volcano Area In The South” Published April 19, 2014, http://latino.foxnews.com/latino/news/2014/04/19/peru-evacuates-28000-llamas-alpacas-from-active-volcano-area-in-south/.
- Wiki: http://en.wikipedia.org/wiki/Ubinas
- Source: http://ovi.ingemmet.gob.pe/portal_volcan/index.php/volcan-ubinas/geologia
- Thouret et al., 2005, Ubinas: the evolution of the historically most active volcano in southern Peru., Bull Volcanol, 67, p. 557-589
- IRIS: http://www.iris.edu/hq/
- MODIS sensor heat sources: http://modis.higp.hawaii.edu/cgi-bin/modis/modisnew.cgi
- Ubinas, Volcano World: http://volcano.oregonstate.edu/ubinas