Ignimbrite Boulder. Matahina Dam. Bay of Plenty. New Zealand.
S 38° 06.845 E 176° 49.190
60H E 484206 N 5781512
This huge 20 tonne ignimbrite boulder is on display at the Matahina Dam in the Bay of Plenty.
Waymark Code: WM9A67
Location: North Island, New Zealand
Date Posted: 07/20/2010
Views: 7
The boulder sits at the Dam wall, a huge solitary boulder of ignimbrite rock, with a bronze plaque describing its presence here.
The boulder is unlike any other rock used in the building of the earth dam, it was excavated during the 1998 strengthening project at the Matahina Dam. It consists of ignimbrite which is a volcanic rock, and probably originated in an upstream gorge of the Rangitaiki River before being carried to this location by successive flooding over several thousand years.
Matahina Earth Dam: Construction on a hydroelectric dam began in 1959. The power station was commissioned in 1967. Te Mahoe village, still in existence, was built for dam construction workers. The dam was in a geologically unsound location – between 1967 and 1987 it shifted downstream almost 1 metre and moved another 150 mm after the 1987 Edgecumbe earthquake (magnitude 6.3). The dam was later strengthened. There were extensive consultations with the Ngati Awa tribe, who were prominent in the completion ceremony in August 1998.
On 2nd March 1987 an earthquake of magnitude 6.25 on the Richter scale struck the Bay of Plenty. The earthquakes epicentre was approximately 23km from the power station with a focal depth of 12km. The dam survived the earthquake but both the right and left abutments were damaged, resulting in a 7 month multi-million dollar repair program.
Type of Display: Geological
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