A seismic refraction experiment southeast of Ruapehu volcano

100

To understand the tectonic evolution of the southern termination of the Taupo Volcanic Zone (TVZ), New Zealand, we compare the late Quaternary structure and kinematics of the southern part of the Taupo Rift or Taupo Fault Belt (Mt Ruapehu Graben) with central parts of the rift (Ngakuru Graben), and with the South Wanganui Basin. We also investigate the differences between displacements of Pliocene and late Quaternary markers within the southern Taupo Rift. Comparison of fault displacement rates derived from displacements of late Quaternary and Pliocene markers yields a preliminary estimate of <400 000 yr for fault initiation of the majority of faults in the southern Taupo Rift. The timing of the onset of faulting in the southern TVZ appears to be younger than central parts of the TVZ and may indicate a step-wise southward propagation of the rift. Faulting also appears to be less evolved in the south than in the central parts of the Taupo Rift (thicker seismogenic crust and hence wider fault spacing), reinforcing the impression of a recent incremental propagation of the Taupo Rift to the south. The onset of faulting coincides with independent observations of the initiation of volcanism in the southern TVZ. We propose that the termination of the TVZ, geographically short of the limit of the Hikurangi margin, may only be temporary, and it is most likely to propagate southward in association with future major perturbations in the subduction margin, such as the occurrence of large ignimbrite volcanism.

Section: Mt Ruapehu Grabenmentioning

confidence: 99%

“…4, point SP2). We have not plotted this contact to the west of Sissons & Dibble's (1981) location (i.e., SP2, Fig. 4) because of lack of local detailed geophysical studies.…”

Section: Mt Ruapehu Grabenmentioning

confidence: 99%

Evolution of the southern termination of the Taupo Rift, New Zealand

Villamor¹,

Berryman

2006

100

“…Surfaces A, B, and C therefore probably ceased aggrading c. >20 000 yr BP and were subsequently deflated between c. 20 000 and 15 000 yr BP, producing a disconformity on them at the base of the coverbeds, which is not present on D. Movement along the Desert Road Fault (Sissons & Dibble 1981), and uplift of the eastern block at this time, deflected the youngest lahars away from surfaces A, B, and C and onto D. The lower downfaulted surface D continued to aggrade until 15 000 yr BP.…”

Section: Distributionmentioning

confidence: 99%

“…Based on known deposit exposure and the regional topography, we can map the lahar surface west and east of the Desert Road Fault (Sissons & Dibble 1981) and Whangaehu escarpment (Fig. 2), and south to Waiouru.…”

Section: Distributionmentioning

confidence: 99%

Late Quaternary constructional history of the southeastern Ruapehu ring plain, New Zealand

Donoghue

Neall

2001

“…Beyond the cone, the river disgorges onto a broad laharic and fluvial fan. The Whangaehu fan is 6 km long and up to 4.5 km wide (Palmer et al 1993); its base is truncated by the scarp of the north-south-trending Desert Road Fault (Sissons & Dibble 1981), at which point the riv er flows within a shallow channel to c. 42 km from the source. Beyond 42 km the river is confined to a deeper channel.…”

Section: Settingmentioning

confidence: 99%

1995 Ruapehu lahars in relation to the late Holocene lahars of Whangaehu River, New Zealand

Cronin

Hodgson

Neall

et al. 1997

Observations of active flows, their deposits, and the effects of lahars generated during the 1995 eruptions of Ruapehu are compared to those of the last 2000 years. The 1995 lahars were generated by similar mechanisms, and had similar volumes and flow rheologies, to those of the last 135 years. However, the large number of lahars in the 1995 sequence and the eventual emptying of the entire Crater Lake on Mt Ruapehu by lahars is distinctive in the context of the historic record. The 1953 and 1975 lahars, although of smaller total volume than the largest 1995 lahar, had higher peak discharges and consequently greater effects on life and property within 57 km from the source. This implies that failure of a lake dam is the most efficient mechanism for generating a fast lahar with high peak discharge, and that eruptions through Crater Lake are more efficient at generating a lahar with high peak discharge when the lake is full.The scant 1995 lahar deposits preserved indicate that the geological record of lahars is likely to be incomplete and biased to events of greatest magnitude. Given this limitation, lahars which formed deposits of the prehistoric (>135 years old) Onetapu Formation were of larger magnitude in all respects, and often more concentrated with sediment, than those of the last 140 years (including 1995). In order to generate such events, catastrophic total emptying of Crater Lake is required. Alternatively, some of the events may have been the result of small flank collapses on the eastern slopes of Ruapehu. These larger events are less frequent than small eruption-triggered lahars on Ruapehu, but they may be preceded by little or no warning. Future lahar hazard mitigation strategies in the Whangaehu River should begin with improving the detection and early warning of such flows. G96042