Approximately 260 million years ago, in the Permian age this area
was part of a massive volcano that had its origin some 40km SE of
Jervis Bay. The resulting flows make up an area of the south coast
that geologists often refer to as the ‘Gerringong
Volcanics’.
The blowhole latite (Igneous rocks which are formed by
solidification of cooled volcanic rock) is the oldest of several
flows that comprise this area. Other features in the area include
the Wandrawandian Tuffs (sth of Nowra), Saddleback Mountain and
north towards Bombo headland.
The latite which makes up this headland has many flow features
evident including flow banding, parallelism of crystals and
elongated vesicles (spherical cavities in the rock). The rock is
also strongly jointed with the shore platform being a mosaic of
regular five to eight sided blocks.
To log a find for this Earthcache take a photo of you & or
your GPS in front of the blowhole and answer the following
questions. (Email answers via gc.com profile) Please fulfil all
requirements of this cache or your log may be deleted.
- How do you think the blowhole was formed? By erosion, by a
cooling fault or both.
- What might have caused the different colouring in the lava
observed here?
Please be careful when in the area as the ocean can be very
unpredictable. It is possible to stand right up close to the
opening (if you don’t mind getting wet).
I hope you enjoy my first Earthcache.
