Lion Rock, Piha

BY BRUCE HAYWARD (GEOLOGIST)
Accessibility: EASY
Lion Rock from the south at spring low tide.
Look inside the throat of an ancient volcano.
Spindle-shaped volcanic bomb that was erupted molten into the air.
Lion Rock/Whakaari was an important defensive paa of pre-European Maori in the Waitakeres.
Honeycomb weathering (growth of salt crystals) on the outer face of Lion Rock.
The Waitakere Ranges are the greatly eroded remnants of the eastern submarine slopes of New Zealand's largest cone volcano - the Waitakere Volcano, which erupted off and on between about 23 and 15 million years ago. Towards the end of its life the volcano's eastern slopes were pushed up out of the sea and two lines of vents began erupting in the east. Lion Rock is one of the vents on the NW-trending western line that today runs up the west coast of the Waitakeres from Whatipu to O'Neill Beach.
Lion Rock is composed of a jumble of blocks of volcanic breccia and scoriaceous layers that were erupted into the air and later slumped back down into the open throat of the vent. This vent fill was then intruded by tongues of molten lava that came up the plumbing and cooled as irregular bodies of hard andesite rock. The vent had blasted its way through the existing Piha Conglomerate (seen in the cliffs at the south and north ends of Piha Beach) when the surface may have been 100 or so metres above the present level of Lion Rock. Erosion over the last 15 million years has removed all the conglomerate that surrounded the Lion Rock vent and just the contents are left standing up as Lion Rock today.
Spindle-shaped volcanic bomb, south side of Lion Rock at high tide level.
Can you see a spindle-shaped bomb (see photo) in the base of the cliffs of Lion Rock on the south side? How might this have been formed?
Can you distinguish between the broken up volcanic breccia (angular rock fragments glued together to form rock) that slumped back into the volcano's throat from the hard andesite that was intruded up as tongues of molten lava before it solidified?
Why does some of the andesite lava have lots of regular joints (cracks) through it?
Directions/Advisory

From the bottom of the Piha Hill drive past the shop and cafe towards North Piha and when you swing north parallel to the beach, park in the parking area on Marine Parade. On a busy weekend parking is available in the Piha Domain carpark next to the estuary before you reach the beach and dunes. You could also park in the carpark behind the beach at South Piha on quiet days.

Piha is an exposed west coast beach often with large waves and breaking surf. Beware of rogue larger waves surging up the beach and in around the base of Lion Rock especially on stormy days at sea. Piha Stream flows out to sea across the landward side of Lion Rock - after heavy rain it can be in flood and flowing rapidly and crossing it should not be attempted. At normal flow levels you will get you ankles wet wading across it but little more - especially easier when the tide is lower.
Lion Rock has steep-vertical cliffs around it with crumbly rock - do NOT attempt to climb up or down any cliffs. Do not linger near the base of any cliffs, especially any that look crumbly or any that may have people up above. There is a tourist track climbing part way up Lion Rock for the view. If you do climb this, do not leave the track nor attempt to ascend the last dangerous climb to the top, even if you see others doing so.

Google Directions

Click here for Google driving directions

Accessibility: EASY

Visit best at 2 hours either side of low tide but some things can be seen at higher tides or from a distance at high tide. Walk across the beach to the bottom of Lion Rock and look at the clean rock faces at high tide level and just above, from the sand. Nothing extra to see by clambering around the rocks towards the ocean side and this can be dangerous in big seas.

Features
Volcanic Landform Matauranga Maori
Geological Age
Erupted about 17 million years ago. Early Miocene
Zealandia Evolution Sequence
Māui Supergroup (Emergence): 25 – 5 million years ago
Links
Cameron, E.K., Hayward, B.W., Murdoch, G., 2008. A field guide to Auckland. Exploring the region's natural and historic heritage., 2nd ed. Godwit, Auckland. p.174