Breakout flood from an ignimbrite-dammed valley after the 5 ka Numazawako eruption, northeast Japan

Abstract

Numazawa volcano in northeast Japan erupted most recently at ca. 5 ka, forming a 2-km-diameter caldera and emplacing at least 4 km 3 of valley-confi ned ignimbrite. The ignimbrite dammed the Tadami River to a depth of >100 m, temporarily impounding >1.6 km 3 of water. Overtopping of the barrier triggered breaching and catastrophic release of the dam lake. Pyroclastic material redeposited by the ensuing fl ood is widely distributed along the Tadami and Agano Rivers in deposits tens of meters thick as far as the coastal Niigata Plain >150 km downstream of the volcano. Evidence for damming and fl ooding found along the rivers includes (1) fi ne-grained, thinly laminated lacustrine deposits upstream of the pyroclastic blockage; (2) 30-m-thick, pumiceous debris-fl ow and hyperconcentrated-fl ow deposits that show continuous sedimentation with no major hiatus downstream of the volcano; (3) fi ne-grained slackwater deposits at tributary river mouths; and (4) large fl ood boulders that form lags on stripped ignimbrite surfaces and younger terrace surfaces, or cropping out within hyperconcentrated-fl ow deposits. Paleohydraulic estimation techniques indicate a peak discharge of 30,000-50,000 m 3 /s at the breach point. Burial of Neolithic Jomon settlements by fl ood and volcaniclastic aggradational deposits at distal locations indicates that such indirect volcanogenic hazards are signifi cant, even where direct primary consequences of volcanic eruptions are minor or absent.

Photogrammetry-based Texture Analysis of a Volcaniclastic Outcrop-peel: Low-cost Alternative to TLS and Automation Potentialities using Haar Wavelet and Spatial-Analysis Algorithms

“…Kataoka et al (2008) have described in details an outburst flood from a temporal dam lake formed in the Tadami River valley by the Numazawako ignimbrite emplacing eruption and its geomorphic impacts around the volcano, including the flood terraces in the Tadami River, from which the material used in the present contribution has been extracted (Cf. Figure 9 in Kataoka et al, 2008). The 290 cm high x 85 cm wide outcrop-peel was extracted from the flood deposits with multiple inversely graded bed sets, rich in rounded pumices indicative of a hyperconcentrated flow deposition (Kataoka et al, 2008).…”

“…Shibahara pyroclastic deposits; the 71 k.a Mukuresawa lava dome; the ~50 k.a Mizunuma pyroclasticflow deposits; the Sozan lava dome of 43 k.a; the Maeyama lava dome of 20 k.a and the Numazawako eruption of 5.4 k.a (Yamamoto, 2007). Kataoka et al (2008) have described in details an outburst flood from a temporal dam lake formed in the Tadami River valley by the Numazawako ignimbrite emplacing eruption and its geomorphic impacts around the volcano, including the flood terraces in the Tadami River, from which the material used in the present contribution has been extracted (Cf. Figure 9 in Kataoka et al, 2008).…”

“…Numazawa Volcano is located on the main island of Japan, Honshu (Figure 1), in the western part of Fukushima Prefecture and about 50 km west of the volcanic front (Yamamoto, 2007;Kataoka et al, 2008). Numazawa Volcano (835 m a.s.l.…”

“…Figure 9 in Kataoka et al, 2008). The 290 cm high x 85 cm wide outcrop-peel was extracted from the flood deposits with multiple inversely graded bed sets, rich in rounded pumices indicative of a hyperconcentrated flow deposition (Kataoka et al, 2008). The deposit is dominated by coarse sand to pebble size material.…”

Luminescence dating of volcanogenic outburst flood sediments from Aso volcano and tephric loess deposits, southwest Japan

“…Numazawa and Towada volcanoes, Japan (Kataoka et al, 2008;Kataoka, 2011), Aniakachak volcano, Alaska (Waythomas et al, 1996), Laacher See volcano, Germany (Park and Schmincke, 1997) and Taupo volcanic zone, New Zealand (Manville et al, 1999). In this study, we apply luminescence dating for the first time to volcanogenic outburst flood sediments from Aso volcano (Takuma gravel bed) and also to the overlying tephric loess deposits to constrain the age of the possible intra-caldera lake outburst event.…”