The c. AD 1315 syn‐eruption and AD 1904 post‐eruption breakout floods from Lake Tarawera, Haroharo caldera, North Island, New Zealand

Abstract

Breakout floods have resulted from temporary blockage of the Lake Tarawera outlet during and after late Holocene eruptions. The largest flood occurred near the end of the c. AD 1315 Kaharoa rhyolite eruption episode of Tarawera volcano after a fan of reworked volcaniclastic material had blocked the existing outlet channel. The 41 km 2 lake rose to >30 m above its present elevation (298 m) before overtopping and releasing c. 1.7 km 3 of lake water as the outlet was scoured down by >40 m. The resulting flood excavated a 300 m wide, 3 km long spillway between the lake and the c. 70 m high Tarawera Falls, and eroded a 1 km wide valley below the falls. Flood deposits, including sand and gravel bars with clast diameters locally exceeding 10 m, are traceable to 40 km downstream of the breach area. Peak discharge at the breach area was c. 10 5 m 3 /s, judging from breach geometry and lake hypsometry. Maximum clast sizes at 5-10 km downstream from the breach indicate a peak discharge of at least 10 4 m 3 /s in the main river channel. Floodwater also traversed a 3 km wide interfluve to cause massive erosion in an adjacent valley. A similar but smaller fan dam that formed after the AD 1886 Tarawera eruption failed in AD 1904, generating a much smaller flood of c. 700 m 3 /s.

Monitoring the Effects of Pulp and Paper Effluent Is Restricted in Genetically Distinct Populations of Common Bully (Gobiomorphus cotidianus)

“…These fish, including the common bully, were obtained from the Waikato River near the West coast of the North Island (24). Given the barrier of Tarawera Falls, it is not surprising that gene flow into the lake is limited, whereas there is ample opportunity for significant downstream (oneway) gene flow, probably assisted by a number of floods caused by the collapse of the lava flow that forms Lake Tarawera (25). Given the volcanic history, recolonization of the lower river reaches by diadromous common bullies may also have occurred.…”

Proximal stratigraphy and event sequence of the c. 5600 cal. yr BP Whakatane rhyolite eruption episode from Haroharo volcano, Okataina Volcanic Centre, New Zealand

“…A drowned tree found in upright growth position within Lake Tarawera, where the lake floor is now at 30 m depth (at U16/082289), has a 14 C age of 5090 ± 100 yr BP (NZ4930, Table 2). The >30 m rise in lake level required to drown and preserve the tree was caused by damming of the earlier and lower outlet from the Lake Tarawera basin by the Tapahoro lava flows (Hodgson & Nairn 2005).…”

Volcanic Generation of Tsunamis: Two New Zealand Palaeo-Events

“…The lake has varied significantly in extent and depth over the last 300 ka, with the present-day extent forming after the 5.6 ka Whakatane Eruption. The deposits from the Whakatane Eruption appear to overlie a palaeosol with trees in growth position >30 m (~270 m asl) below present lake level at 298 m asl (Hodgson and Nairn, 2005), and produce a distinctive horizon in seismic reflection images of the lake sediments (Davy and Bibby, 2005). After the Whakatane Eruption, Lake Tarawera rapidly rose to an elevation >330 m asl, forming extensive terraces around the lake, before falling slowly to an elevation of ~315 m asl at the time of the Kaharoa Eruption (Hodgson and Nairn, 2005).…”

“…The deposits from the Whakatane Eruption appear to overlie a palaeosol with trees in growth position >30 m (~270 m asl) below present lake level at 298 m asl (Hodgson and Nairn, 2005), and produce a distinctive horizon in seismic reflection images of the lake sediments (Davy and Bibby, 2005). After the Whakatane Eruption, Lake Tarawera rapidly rose to an elevation >330 m asl, forming extensive terraces around the lake, before falling slowly to an elevation of ~315 m asl at the time of the Kaharoa Eruption (Hodgson and Nairn, 2005). The 1314±12 AD Kaharoa Eruption is a key stratigraphic marker for New Zealand as it coincides with the earliest evidence of human occupation (Hogg et al, 2003).…”

“…Davy and Bibby (2005) did not identify Kaharoa pyroclastic flows in their seismic reflection surveys, but they did not approach closer than 100 m to the shore and did not have a shallow seismic survey in the area affected by the pyroclastic flows. Hodgson and Nairn (2005) state that the lake level fell to <303.5 m asl during the initial explosive phase of the eruption, before rising ~30 m after the eruption due to damming of the lake outlet by the eruptive deposits. They suggest that this abrupt fall was due to tsunami waves overtopping the natural pre-eruption dam, and scouring out a deeper outlet channel.…”