Opunake Boat Ramp

Opunaki Sea Cliff, Photo J.Thomson @ GNS Science
Excellent cliff sections that show a clean slice through some of Egmont Volcano's lahars and debris flow deposits.
Opunaki Sea Cliff, Photo J.Thomson @ GNS Science
The cliffs consist of deposits of volcanic debris that originally flowed down the southwest side of Egmont Volcano during or following periods of volcanic activity. A large part of the ring plain surrounding Egmont volcano is made up of similar material. The layers consist of lahars (water-born debris flows) and even an avalanche resulting from collapse of part of the volcanic cone.
Opunaki Sea Cliff, Photo J.Thomson @ GNS Science
There are lots of interesting features to be spotted in these cliffs that help us to interpret the way they were deposited.
Firstly, have a close look at the types of rock that make up these deposits, you will see that they are mostly fragments of hard, dense, crystalline volcanic rock. This suggests they originated as lava or ash from Egmont Volcano.
Look out for graded bedding (when the particles get smaller upwards within a layer), channelling (when one layer has been scooped out and eroded, before the next layer is deposited on top of it), how rounded or angular the particles are (very angular particles have not travelled far from their source) and the range of particle sizes (large particles take more energy to be transported than smaller ones.
See if you can identify individual lahars by taking a step back and looking for repetition of layers from bottom to top of the cliff.
At the very top of the cliff, in between the vegetation, you may notice a layer of large, poorly sorted boulders and rock fragments. This is interpreted as a huge rock avalanche deposit resulting from the partial collapse of the volcanic cone about 5000 - 7000 years ago.

The boat ramp at Opunake is directly accessible by car, with easy parking.

An easily accessible outcrop.

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Accessibility: WHEELCHAIR

You can study the cliffs directly from the car park

Sedimentary Volcanic
Geological Age
These cliffs are a few tens of thousands of years old (Pleistocene), which is very young in geological terms.
Zealandia Evolution Sequence
Pākihi Supergoup: 5 million years ago – present
Check out this video about the erosion processes of Taranaki Volcano, and the resulting sediments in the surrounding area: (9m 20s) https://youtu.be/ehK0oPgWYjA Geological QMap and report for Taranaki: http://www.gns.cri.nz/Home/Our-Science/Earth-Science/Regional-Geology/Geological-Maps/1-250-000-Geological-Map-of-New-Zealand-QMAP/QMAP-text-maps#taranaki