Stratigraphy, age, and correlation of voluminous debris avalanche events from an ancestral Egmont Volcano: implications for coastal plain construction and regional hazard assessment

Abstract Two previously unrecognised debris‐avalanche deposits have been identified on the eastern flanks of Egmont Volcano beneath a thick mantle of tephric and andic soil material that has mostly subdued their topographic expression. The Ngaere Formation is a c. 23 14C ka large volume (>5.85 km3) debris‐avalanche deposit that is widely distributed over 320–500 km2 of the north‐east, south‐east, and south portions of the Egmont ring plain. The second deposit, Okawa Formation, is a c. 105 ka large volume (>3.62 km3) debris‐avalanche deposit that has been mapped over a minimum area of 255 km2 in northern and north‐eastern Taranaki. Both debris‐avalanche formations contain axial facies with hummocks composed mainly of block‐supported brecciated andesitic debris. A less conspicuous marginal facies, texturally resembling a mudflow, is more extensive. A third debris‐avalanche deposit (Motunui Formation) is extensively preserved along the north Taranaki coast where it is truncated by a c. 127 ka wave cut surfac...