Deposits of a rapidly eroding meandering river: Terrace cut and fill in the Taupo Volcanic Zone

Abstract

River terraces in a section of the upper Rangitaiki River have formed in the last 1850 years as the river rapidly regrades following a major volcanic eruption (Taupo Tephra Formation). Terrace treads are cut at the migrating outside edge of meander loops and are subsequently filled by scroll and point bar deposits associated with the same loop. Entrenchment rates as high as 5 mm/yr cause the meanders to be permanently abandoned following cutoff. This results in the widespread preservation of fluvial cover sequences up to 6 m thick in an otherwise strongly erosive regime.

Keywords:

• river terraces
• meander loops
• cut and fill
• Taupo Pumice Alluvium