Latitude -34.671981, Longitude 150.863225
Located in the Illawarra Region of NSW, nearest large town Kiama
The Blow Hole at Kiama was first remarked upon by explorer George Bass in 1797. Bass was investigating the NSW south coast and, on hearing a booming noise, went ashore to investigate. The Kiama Blow Hole is now one of the most famous geological sites in the Illawarra region. The Blow Hole was excavated out by the sea, along the line of a dyke in the Permian Blow Hole Latite (the base foundational rock in the area). A long sea cave was hollowed out along the dyke and then collapsed through to the surface at its landward end. When waves or sea surge pushes water into this cave, compressed air at the end may force spray up through the hole, sometimes to quite a considerable height. The activity of the Kiama Blow Hole varies greatly, and depends on sea conditions for the height of its spray.
The Blow Hole Latite is one of a number of latite lava units (alkali rich igneous rocks of basaltic appearance) in the volcanic sequence at Kiama (Gerringong Volcanics). The Blow Hole Latite is the basal volcanic unit in the sequence. Whether the latite units are all submarine flows or were sometimes intrusive sheets into soft Permian sediments, has been the continuing subject of some considerable study. Earlier opinions tended to regard them as sills but later investigators believed they were extrusive and consist of submarine flows. Pillow lava structure has been found in both the Blow Hole and Bumbo Latites. Extensive brecciation effects are associated with the lavas.
Latitude -34.686799, Longatude 150.859129
The Little Blow Hole is situated south of the main Blow Hole headland, lying at the northern side of Marsden Head, off Tingira Drive at Kiama. The Little Blowhole is on the rocky shoreline and its operation is more regular than at the main Blow Hole. The latite here is columnar jointed and the spray comes up through an opening in the latite where one of the columns has collapsed into an underlying sea cave eroded from a basalt dyke. The latite here shows pronounced flow features, such as crystal alignment, flow banding and elongation of vesicles (gas cavities).
Both of the Blowholes are located in Kiama on the South Coast of NSW. The main Blow Hole is located on Blowhole Point and the Little Blowhole is located on Marsden Head.