[3] The graben extends on shore from the west of the town of Kawerau to the coast at Matatā in the north and Whakatāne in the south.

[3] The graben has formed where the Australian Plate's southwest–northeast trending North Island Fault System is intersected by the northeast-trending Taupō Rift and is on a graywacke basement.

It is a site of continuing late Quaternary extension and subsidence, containing dacitic to andestitic volcanoes,[8] and is otherwise filled with oceanic and river sediments as well as rhyolitic volcanics to over 2 km (1.2 mi) in depth.

[12] Nearby caldera volcanism has produced rhyolitic tephra and ignimbrite deposits that are very deep towards the south western end of the graben.

To the west Castlecliffian (mid Quaternary) marine sediments have been elevated at a rate of 1 mm (0.039 in)/year to more than 300 m (980 ft) above sea level.

On present land there have been significant earthquake ruptures in the last 800 years in each of the three most active fault zones associated with the graben.

[3] The off shore underlying volcanic sills noted above are consistent with a tectonomagmatic relationship, where magmas supplied by flux melting in the mantle wedge thermally weaken the lithosphere and facilitate rifting.