From earthquakes to volcano territory - pahoehoe - "ropy" lava

Here I am in Auckland for a brief visit.  Coming in from the airport along a leisurely scenic route to enjoy aspects of the Manukau Harbour we passed what used to be oxidation ponds (500 hectares!) used for treating sewage - now being rehabilitated, with extensive native plantings on the affected shoreline (13km!) already looking great.  I had no idea they had been so extensive.  The Mangere Wastewater Treatment Plant now uses land-based technology (reactor clarifiers and ultraviolet filtration) which takes only 13 hours to process the wastewater.  That is a great development for all kinds of environmental and cultural reasons.

Further along the shoreline, on Kiwi esplanade near the Mangere bridge, there was another surprise.

The still waters of the Manukau - it is a sheltered harbour, with fine mud rather than sand along the shore - but the bright and contrasty noon light revealed some ridges, fissures and lumps.

It doesn't take long to be reminded that New Zealand is a geologically active place.  These dark rocks and ridges are volcanic rock - lava flows from nearby Mangere mountain.  There is a Hawaiian term describing a type of lava flow with a surface that has a ropy appearance - it develops where very fluid lava has continued to flow beneath a flexible crust, which twists and wrinkles into ridged shapes.

It is called pahoehoe.  It is slightly obscured by the mud, but I can still imagine the dark lava flow buckling and ridging - like the images of active Hawaiian lava fields that are so dark and dramatic.

And these dark rocks are scoria.  I am more accustomed to seeing scoria in Auckland - which is, after all, built on a dormant volcanic field of monogenetic (they erupt only once) volcanoes.  Scoria has a vesicular appearance from gas bubbles, whereas the smoother lava rock which you can see in the background was not gas-charged.  Glasswort, which I have described in other posts, is growing on this not-very hospitable base. 

Leaving the shakes behind, I am reminded of other aspects of the awesome activity of this earth.