Youngest volcanic rocks

Unit symbol: Qv
Age range Quaternary and latest Tertiary? (1.806 to 0 Ma)
Lithology: Igneous - Volcanic
Group name: Young volcanic and shallow intrusive rocks
Volcanic rocks ranging in composition from rhyolite to basalt. Along the Aleutian magmatic arc and the Wrangell Mountains, the rocks are predominantly andesite and lesser dacite and basalt of calc-alkaline and tholeiitic affinity in lava flows, volcanic breccia, lahar deposits, and debris-flow deposits. Lava flows and clasts in other volcanic deposits of unit are porphyritic, typically glassy, gray to black, and commonly vesicular. Unit also includes basaltic, basaltic andesite, and dacite parasitic cinder and spatter cones. Unit typically forms volcanic edifices; it also forms isolated outcrops that cap ridges, providing a good example of topography reversal, which results from erosion of surrounding country rocks, leaving exposed more erosion-resistant flows that formerly had occupied valleys. Individual flows are locally as thick as 30 m and are laterally continuous over large areas. Includes Edgecumbe Volcanics (basalt, andesite, and dacite) on Kruzof Island (Loney and others, 1975; Riehle and others, 1989) and unnamed basaltic to rhyolitic rocks on islands west of Prince Wales Island (Eberlein and others, 1983), and on Zarembo, Kuiu, and Kupreanof Islands (Brew and others, 1984). Rocks of Holocene age were recognized east of Wrangell Island (Elliott and others, 1981) and on Kruzof Island (Loney and others, 1975), and basaltic rocks of Holocene and (or) Pleistocene age are found on southern Kupreanof Island (Brew and others, 1985). On Revillagigedo Island and mainland to the east in the Ketchikan quadrangle (Berg and others, 1978, 1988) and at many other localities in southeast Alaska (Karl and others, 2012), this extrusive unit consists of alkaline-olivine basalt that forms volcanic cones, columnar jointed lava flows, and rubble flows that contain pumice and scoria; it also includes lenses of ash and lapilli a few centimeters to a few meters thick—too small to show on the map. Includes postglacial flows and pyroclastic deposits that overlie glacial deposits and landforms

Source map information

Source map Wilson, F.H., Detterman, R.L., and DuBois, Gregory, 1999, Digital data for the geologic framework of the Alaska Peninsula, southwest Alaska, and the Alaska Peninsula terrane: U.S. Geological Survey Open-File Report 99-317. [http://geopubs.wr.usgs.gov/open-file/of99-317/]
Symbol Qv
Unit name Volcanic rocks
Description Andesite, dacite, and leucobasalt lava flows, volcanic breccia, lahar deposits, and debris-flow deposits. Lava flows and clasts in other volcanic deposits of unit are porphyritic, typically glassy, gray to black, and commonly vesicular. Andesite is overwhelmingly dominant composition and probably constitutes 60 percent or more of rocks. Includes basalt of Black Point, Arch Point Basalt, and Dushkin Basalt (Kennedy and Waldron, 1955), and Frosty Peak Volcanics (Waldron, 1961). Also includes lava flows, breccias, and older pyroclastic deposits of Yantarni Volcano (Riehle and others, 1987). Unit typically forms volcanic edifices; it also forms isolated outcrops that cap ridges, providing a good example of topography reversal caused by erosion. Individual flows are locally as thick as 30 m and are laterally continuous over large areas. Unit also includes basaltic, basaltic andesite, and dacite parasitic cinder and spatter cones. Cones are commonly 30 to 300 m high, are steep sided, and have small crater at top. Rocks at Mount Veniaminof are mainly basaltic andesite, whereas those at Aniakchak Crater are mainly dacite (T.P. Miller, oral commun., 1990). Basaltic scoria cones occur at three separate locations in the Mount Katmai 1:250,000-scale quadrangle (Riehle and others, 1993). Rocks are highly scoriaceous to vitrophyric, ranging in size from cinder-size fragments to 1-m-long bombs (Detterman and others, 1981b; T.P. Miller, oral commun., 1991). Primarily located in vicinity of Mount Veniaminof, Aniakchak Crater, in Mount Katmai area, and on Unimak Island
Lithology Igneous

Correlated geologic units

Label Qv
Description Volcanic rocks, undivided
Geologic age Pleistocene to Holocene
Geologic setting Extrusive
Lithology Form Importance
Felsic-volcanic < Volcanic < Igneous Flow Major
Mafic-volcanic < Volcanic < Igneous Flow Major
Volcanic < Igneous Pyroclastic Indeterminate, major
Mafic-volcanic < Volcanic < Igneous Pyroclastic Indeterminate, major