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Naranjo, José A.; Stern, Charles R.
Tephra deposits exposed in road-cuts in both Chile and Argentina between approximately 42°30' to 45°S preserve evidence of four small (VEI <3 and volume <0.15 km³) and seven medium size (VEI = 3-5 and volume between 0.15 to 1 km³), or possibly larger, explosive Holocene eruptions of seven of the eight stratovolcanoes in this southernmost segment of the Andean Southern Volcanic Zone (SVZ). These eruptions include one from the Chaitén volcano at approximately 9,370 BP, two from the Michinmahuida volcano occurring at <6,350 BP and <3,820 BP, three from the Corcovado volcano with the oldest one occurring sometime between <9,190 and 7,980 BP and the two younger ones at <7,980 BP and <6,870 BP, one from the Yanteles volcano at <9,190, two from the Melimoyu volcano occurring at <2,740 BP and <1,750 BP, one from the Mentolat volcano at <6,960, and one from the Macá volcano at approximately <1,540 BP. The principal orientation, to the east, of the tephra plumes produced by these Holocene explosive eruptions in this arc segment, indicates a possible impact for future explosive eruptions on aeronavigation routes in Argentinean Patagonia. The total of eleven small and medium size explosive eruptions over a period of about 8,000 years implies a frequency of one eruption approximately every 725 years in this segment of the Andean SVZ, with each of the eight volcanoes having produced on the average 1.4 eruptions during the Holocene. This is about as frequent as for similar size eruptions from individual volcanic centers further north in the SVZ. In contrast, the Hudson volcano, the southernmost volcano in the SVZ, located just north of the Chile Rise-Trench triple junction at 46°S, has had three very large and nine other documented small explosive Holocene eruptions, and thus both larger and more numerous explosive Holocene eruptions than all the other centers in the southernmost SVZ combined. Hudson volcano may be significantly more active than the other centers in the southernmost SVZ because of its location close to the triple junction.