Ubinas: the evolution of the historically most active volcano in southern Peru

Ubinas volcano has had 23 degassing and
ashfall episodes since A.D. 1550, making it the historically most active volcano in southern Peru. Based on fieldwork, on interpretation of aerial photographs and satellite images, and on radiometric ages, the eruptive history of Ubinas is divided into two major periods.
Ubinas I (Middle Pleistocene 376 ka) is characterized by lava flow activity that formed the lower part of the edifice.
This edifice collapsed and resulted in a debris-avalanche deposit distributed as far as 12 km downstream the Rio Ubinas. Non-welded ignimbrites were erupted subsequently
and ponded to a thickness of 150 m as far as
7 km south of the summit. These eruptions probably left a small collapse caldera on the summit of Ubinas I. A 100-m thick sequence of ash-and-pumice flow deposits followed,
filling paleo-valleys 6 km from the summit. Ubinas II, 376 ky to present comprises several stages. The summit cone was built by andesite and dacite flows between 376 and 142 ky. A series of domes grew on the southern flank and the largest one was dated at 250 ky;
block-and-ash flow deposits from these domes filled the upper Rio Ubinas valley 10 km to the south. The summit caldera was formed between 25 and 9.7 ky. Ash-flow deposits and two Plinian deposits reflect explosive eruptions
of more differentiated magmas. A debris-avalanche
deposit (about 1.2 km3) formed hummocks at the base of the 1,000-m-high, fractured and unstable south flank before 3.6 ka. Countless explosive events took place inside the summit caldera during the last 9.7 ky. The last Plinian
eruption, dated A.D.1000-1160, produced an andesitic pumice-fall deposit, which achieved a thickness of 25 cm 40 km SE of the summit. Minor eruptions since then show phreatomagmatic characteristics and a wide range in
composition (mafic to rhyolitic): the events reported since A.D. 1550 include many degassing episodes, four moderate (VEI 2-3) eruptions, and one VEI 3 eruption in A.D. 1667.
Ubinas erupted high-K, calc-alkaline magmas (SiO2=56 to 71%). Magmatic processes include fractional crystallization and mixing of deeply derived mafic andesites in a shallow magma chamber. Parent magmas have been relatively
homogeneous through time but reflect variable
conditions of deep-crustal assimilation, as shown in the large variations in Sr/Y and LREE/HREE. Depleted HREE and Y values in some lavas, mostly late mafic rocks, suggest contamination of magmas near the base of
the >60-km-thick continental crust. The most recently erupted products (mostly scoria) show a wide range in composition and a trend towards more mafic magmas.
Recent eruptions indicate that Ubinas poses a severe threat to at least 5,000 people living in the valley of the Rio Ubinas, and within a 15-km radius of the summit. The threat includes thick tephra falls, phreatomagmatic ejecta,
failure of the unstable south flank with subsequent debris avalanches, rain-triggered lahars, and pyroclastic flows.
Should Plinian eruptions of the size of the Holocene events recur at Ubinas, tephra fall would affect about one million people living in the Arequipa area 60 km west of the summit.

Allégre CJ, Provost A, Jaupart C (1981) Oscillatory zoning: a pathological case of crystal growth. Nature 294:223-228

Bullard FM (1962) Volcanoes of southern Peru. Bull Volcanol. 24:443-453

Barazangi M, Isacks B (1976) Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America. Geology 4:686-692

Bourdon B, Worner G, Zindler A (2000) U-series evidence for crustal involvement and magma residence times in the petrogenesis
of Parinacota Volcano, Chile. Contrib Mineral Petrol 139(4):458-469

Davidson JP, de Silva S (2000) Composite volcanoes. In: Sigurdsson H et al (eds) Encyclopedia of volcanoes. Academic Press, San Diego, pp 663-681

Davidson JP, McMillan NJ, Moorbath S, Worner G, Harmon RS,Lopez Escobar L (1990) The Nevados de Payachata volcanic region (18°S/69°W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism. Contrib Mineral Petrol 105:412-432

de Silva SL, Francis PW (1991) Volcanoes of the Central Andes. Springer, Berlin Heidelberg New York, pp 216

de Silva SL, Davidson JP, Croudace IW, Escobar A (1993) Volcanological and petrological evolution of volcan Tata Sabaya,SW Bolivia. J Volcanol Geotherm Res 55:305-335

Feeley TC, Hacker MD (1995) Intracrustal derivation of Na-rich andesitic and dacitic magmas: an example from volcan Ollague,
Andean central volcanic zone. J Geol 103:213-225

Finizola A, Sortino F, Lénat JF, Macedo O, Gonzales K, Ramos D (1998) SP studies of hydrothermal systems and structure on
Misti and Ubinas volcanoes, south Peru. In: Second International Workshop on Magnetic and EM Methods in Seismology and Volcanology, Chania, Greece (Abstract)

Finizola A, Sortino F, Lénat JF, Valenza M (2002) Fluid circulation at Stromboli volcano (Aeolian Islands, Italy) from self-potential and CO2 surveys. J Volcanol Geotherm Res 116(1-2):1-18

Finizola A, Sortino F, Lénat JF, Aubert M, Ripepe M, Valenza M (2003) The summit hydrothermal system of Stromboli: new insights from self-potential, temperature, CO2 and fumarolic
fluids measurements with structural and monitoring implications. Bull Volcanol 5:486-504

Gerbe MC, Thouret JC (2004) Role of magma mixing in the petrogenesis of lavas erupted through the 1990-1998 explosive activity of the Nevado Sabancaya in southern Peru.
Bull Volcanol 66:541-561

Ginibre C, Kronz A, Worner G (2002) Minor and trace element zoning patterns in volcanic plagioclase: examples for crystalchemical,
compositional and kinetic control and implications
for magma chamber processes. Contrib Mineral Petrol 143:300-315

Green TH (1972) Crystallization of calc-alkaline andesite under controlled high-pressure hydrous conditions. Contrib Mineral Petrol 34:150-166

Hantke G, Parodi I (1966) The active volcanoes of Peru. Catalogue of the active volcanoes of the world including solfatara fields,Part XIX, Colombia, Ecuador and Peru. Internat Assoc, Volcanol,Rom 65-73

James ED (1982) A combined O, Sr, Nd, and Pb isotopic and trace element study of crustal contamination in central Andean lavas,
I. Local geochemical variations. Earth Planet Sci Lett 57:47-62

Juvigné E, Thouret JC, Gilot E, Gourgaud A, Legros F, Uribe M,Graf K (1997) Etude téphrostratigraphique et bioclimatique du
Tardiglaciaire et de l'Holocène de la Laguna Salinas, Pérou méridional. Géogr phys Quat 51(2):219-231

Lipman PW (1997) Subsidence of ash-flow calderas: relation to caldera size and magma-chamber geometry. Bull Volcanol 59:198-218

Mahlburg-Kay S, Mpodozis C, Coira B (1999) Neogene magmatism,tectonism, and mineral deposits of the central Andes (22° to 33° S latitude). In: Skinner BJ (ed) Geology and ore deposits
of the central Andes. Soc Econ Geol Spec Publ 7:27-59

Marocco R, del Pino M (1966) Geologia del Cuadrangulo de Ichuna. Comision carta geologica nacional, Bol 14: pp. 57 and 1 colour map (1/100,000 scale)

Morimoto N, Fabries J, Fergusson AK, Ginzburg IV, Ross M,Seifert FA, Zussman J, Aoki K, Gottardi G (1988) Nomenclature of pyroxenes. Bull Mineral 111:535-550

Nakamura M, Shimakita S (1998) Dissolution origin and syn-entrapment compositional changes of melt inclusions in plagioclase.
Earth Planet Sci Lett 161:119-133

NCEP-NCAR (1998) National Center for Environmental Prediction-National Center for Atmospheric Research, Climate Data Assimilation System, Reanalysis Project, monthly mean data
from the period 1979-1995. http://www.gfdl.gov/jjp/ncap_-data.html

Papike JJ, Cameron KL, Baldwin K (1974) Amphiboles and pyroxenes:characterization of other than quadrilateral components and estimates of ferric iron from microprobe data (Abstract).
Geol Soc Am Abstracts with Programs 6:1053-1054

Renne PR, Swisher CC, Deino AL, Karner BD, Owens T, DePaolo DJ (1998) Intercalibration of standards, absolute ages and uncertainties
in 40Ar/39Ar dating. Chem Geol, Isotope Geosci Sect 145(1-2):117-152

Rivera M, Thouret JC, Gourgaud A (1998) Ubinas, el volcan mas activo del sur del Perffl desde 1550: Geologia y evaluacion de las amenazas volcanicas. Bol Soc Geol Perffl 88:53-71

S brier M, Soler P (1991) Tectonics and magmatism in the Peruvian Andes from Late Oligocene time to the Present. Geol Soc Am Spec Pap 265:259-277

Seltzer G (1990) Recent glacial history and paleoclimate of the Peruvian-Bolivian Andes. Quat Sci Rev 9:137-152

Simkin T, Siebert L (1994) Volcanoes of the world-a regional directory, gazeteer and chronology of volcanism during the last 10,000 years, 2nd edn. Global Volcanism Program. Smithsonian Institution, Washington, DC pp 348

Singer B, Dungan MA, Layne GD (1995) Textures and Sr, Ba, Mg,Fe, K, and Ti compositional profiles in volcanic plagioclase:clues to the dynamics of calc-alkaline magma chambers. Am Mineral 80:776-798

Steiger RH, Jaeger E (1977) IUGS Subcommission on geochronology:convention on the use of decay constants in geoand cosmochronology. Earth Planet Sci Lett 36:359-362

Sun S, McDonough WF (1989) Chemical and isotopic systematics of oceanics basalts: Implications for mantle composition and processes. Magmatism in the ocean basin. Geol Soc Spec Publ 42:313-345

Thouret JC, Le Pennec JL, Woodman RS Macedo O (1996) Ubinas (Perffl), Increased fumarolic activity prompts seismic and other monitoring. Global Volc Network Bull, Smithsonian Institution,
Washington, DC 7

Thouret JC, Finizola A, Fornari M, Suni J, Legeley-Padovani A,Frechen M (2001) Geology of El Misti volcano nearby the city of Arequipa, Peru. Geol Soc Am Bull 113(12):1593-1610

Thouret JC, Juvigné E, Gourgaud A, Boivin P, D vila J (2002)Reconstruction of the A.D. 1600 eruption at Huaynaputina volcano, Peru, based on the correlation of geologic evidence
with early Spanish chronicles. J Volcanol Geotherm Res 115(3-4):529-570

Tindle AG, Webb PC (1994) Probe-Amph - a spreadsheet program to classify microprobe-derived amphibole analyses. Comp Geosci 20:1201-1228

Valdivia J (1995) Breve resena historica del distrito de Ubinas. Bol consejo de Ubinas, Ubinas, Perffl, pp 40

Worner G, Harmon RS, Davidson J, Moorbath S, Turner D,McMillan N, Nye C, Lopez-Escobar L, Moreno H (1988) The Nevados de Payachata volcanic region (18°S/69°W, N. Chile):I. Geological, geochemical and isotopic observations. Bull Volcanol 50:287-303