The Waitakere Super Volcano, often referred to as the Manukau Volcano, lies 20km off the coast from Piha. The now extinct volcano is estimated to have once stood 3000-4000m tall from the sea floor. The Manukau volcano is about the same size as Lake Taupo.
There was intermittent activity from about 22 million years ago culminating in a violent eruption destroying itself almost entirely some 16 million years ago, making it a much older volcanic feature than the relatively young Auckland volcanic field. The time period of activity from the Manukau volcano makes it a contemporary of the Coromandel volcanoes.
Today, the razor-back ridges, rugged valleys and steep cliffs of the Waitakere Ranges are the remnants of the eastern slopes of this volcano, formed largely of Manukau breccia. Note that the black sand beaches come from elsewhere: titanomagnetite swept up the coast from Taranaki. Most of the remnants of the volcanic island have been eroded away by incessant marine processes and rainwater runoff. This erosion has been interspersed with periods of uplift which are largely responsible for the present height and tilted "flat" top of the ranges.
Pillow Lava
The term 'Pillow Lava' refers to a volcanic formation of bulbous, sperical or tubular lobes of lava formed by an underwater eruption with a relatively low effusion rate. As the magma erupts and makes contact with the water, a solidified crust forms around the molten core which continues to flow.
Slow extrusion gives enough time for a thick crust to form on all sides of a pillow lobe, and prevents individual pillows from coalescing into a sheet. Internally the pillows are fed via a distributary system of interconnected channels. Pillows are not typically hollow and tend to solidify all the way through and often have lineations or scrape marks on their sides that form during extrusion.
Pillow flows are produced by the piling up of individual pillow lava lobes. As a pillow flow forms, the newest pillows are erupted from the top of the stack and flow outward a limited distance before freezing, a process which tends to produce steep-sided mounds or ridges which can grow to be 10's of meters thick.
This Earthcache - Pillows
This earthcache takes you to a stretch of Auckland's west coast where you will find one of the world's finest examples of pillow lava. In the cliffs above the shoreline you will observe a variety of volcanic rock formations resulting from magma eruption underwater including an area of cliff face full of clearly defined pillow lava cross sections.
At a number of spots along the shoreline, you will need to perform certain tasks in order to claim a find log on this earthcache. You will be asked to describe certain features, and these answers should be emailed to the cache owner - they should NOT be included in your online log entry. You will also be asked to take some photos and these should be uploaded with your online log entry. Failure to answer the questions or upload the required photos may result in your online log being deleted.
Do NOT attempt this earthcache at night as you will not be able to see anything, it will be quite dangerous, you will not be able to take any of the required photos, and you will not learn anything.
Also, do NOT attempt this earthcache at high tide, or even medium tide in stormy conditions as it will be too dangerous. Please be careful to watch out for seals as you are climbing around the rocks - always give them a wide berth and never hang around between them and the sea - they are quicker and more dangerous than they look.
Waypoint 1 (S 36 50.191 E 174 25.634): Here you will see some large objects on the beach. Question: Please describe the formations, how you believe they were formed and where they came from. Photo: At this point, also please observe the various formations and textures in the cliff face above you and take a photo of the most interesting shapes you can see. Example photos are shown below, but you must also include your GPS in your photo.
Waypoint 2 (S 36 50.479 E 174 25.695): Here you will find the rock shown in the photos below. This rock is a good example of an underwater magma flow. Notice the outer crust which has formed and then been torn apart by the continuing molten flow, which has then also solidified. Question: Please email the cache owner the approximate dimensions of the exposed portion of the rock.
Waypoint 3 (S 36 50.504 E 174 25.718): From this spot you can observe in the cliff face above you one of the best examples in the world of pillow lava lobes stacked upon each other. Photo: Here you are required to take a photo of the cliff face showing, as best you can, some examples of pillow lava (you can zoom in if you want). Photo: You must also take a photo of yourself and your GPS with the shoreline to the south in the background, from this spot. Question: From the beach, you must also estimate the average size of the pillow lava lobes, and estimate the height of the base rock layer from the level where you are standing, to the layer including exposed pillow lava.
Please email all of the above required answers, for questions relating to WP1, WP2 and WP3, to the cache owner. You can then go ahead and log online immediately and upload the required photos with your online log.
Logs that do not meet the above requirements, or are not accompanied by emails with the correct answers, will face deletion.
You can log this cache straight away after you have emailed your answers to the cache owner, no need to wait for confirmation. Please include the name of this earthcache in the email - you'd be surprised how many people forget. Also, when contacting us with answers, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
Happy Earthcaching!
kiwicouple