[Geysers] Eruption at Ngatamariki, NZ

Ashley Cody ashley.cody at wave.co.nz
Wed Apr 20 20:15:34 PDT 2005

On Tuesday 19th April at 10.30am a hydrothermal eruption occurred at Ngatamariki geothermal field. This is about 5 miles SE from Orakeikorako and about 2 miles S of Waikato river. I visited afternoon of same day and following day again. A previously infilled hydrothermal eruption (HE) crater ~50m dia. had formed in 1947. Until this latest blowout it had been a flowing hot spring. 

However, over past year three new springs had developed around periphery of old crater lake; the latest was 7m dia., 85 deg. C and flowing ~0.5 lps. It formed between Nov 2004 and Feb 2005. 

Tuesday 19th eruption ripped out the whole lake to open a new crater also ~50m dia. and threw debris to ~100m radius of crater rim as a continuous deposit, with blocks <0.2m dia. to ~100m distance and blocks <0.6m dia. to ~50m distance. Deposit up to 4m thick around rim. 

Pine trees <30m away from margin of crater had bark completely stripped off by impact of rocks. About 2 hectares (~5 acres) area converted to a rubbly sandy beach like landscape. Previously dense blackberry and scrub. Orakonui Stream running down alongside this thermal area got dammed and ponded up valley for about three hours until it started to overtop and cut through dam. Stream flow normally about 100 lps (20-25 galls/sec).

Farmer working in field directly alongside  and on top of terrace above the blowout got plastered in fine sandy muds. Many rocks up to 10 cm (~4") landed within about 25m of him. Main blast rapidly weakened; initially must have been debris thrown ~50m high but by 3.00pm debris occiasionally thrown <10m high and on Wed. morning it was strongly boiling <1m high and steaming but no ejecta at all.

I have attached a small thumbnail picture but if this does not get through, I could email directly some pictures to anyone interested.

Ashley Cody
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