This overlying layer is made of an unsorted mixture of different boulders and less coarse particles of rock. You can also find chunks of carbonaceous material scattered within the layer that must have been ripped up into it as it was emplaced. This 4 metre thick layer of material has been mapped over a minimum area of 255 km2 around north Taranaki, and has a total volume of at least 3.6 km3.
Mount Egmont (Taranaki) volcano is the source of this layer. Like some of our other andesitic volcanoes, Mount Egmont is made up of layers of unconsolidated volcanic deposits interbedded with more massive lava flows. Because the slope angle of the volcano is very steep, the cone is inherently unstable, resulting in occasional enormous avalanches of debris launching down the mountainside, spreading across the surrounding countryside and out into the sea for distances of up to 40 km from the source. For this reason Egmont is a significant geological hazard that is monitored by GeoNet.
|Rimu Pollen (Dacrydium cupressum) 43 microns across|
|Cyathea treefern spore, diameter 30 microns|
In the last image you can see that another carbon rich layer formed in a depression at the top of the Okawa Formation (centre left). Above that the rest of the section is made up of orange and pale brown soils.