The Blowhole, Kiama, New South Wales

by | posted in: Landscapes | 10
The Blowhole, Kiama
The Blowhole, Kiama
When we visited the Blowhole at Kiama, south of Sydney in New South Wales, the huge waves were making it erupt with a “whoomp”. People would stand for ages watching the action. It was fun seeing some little kids (and their parents) stand up close on the obviously-wet platform, only to be soaked when an erupting water column dropped on top of them.

The headland is composed of a black basaltic-looking volcanic rock called latite. Called the Blowhole Latite Member, it is up to 50 m thick and displays tall, well developed columns (visible around sea level at the Blowhole). It is exposed along the coast for about 11 km, dipping slightly to the north and dropping below sea level at Kiama. The eruption involved massive volumes of lava.

The volcanic flow sits on a formation called the Westley Park Sandstone Member, sometimes called the Westley Park Tuff because it contains lots of volcanic ash. This displays many sedimentary structures such as bedding, cross bedding and scour and fill—evidence of deposition from flowing water. The contact between the sandstone and the volcanic rock is highly irregular because the sediment and lava had mixed together. The sediment was obviously loose and wet when the lava erupted upon it. A mixture of lava and sediment like this is called peperite.

At the top of the Blowhole Latite Member, the overlying sediment has also mixed with lava forming peperite and this mixing can be seen alongside the path. The overlying member is called the Kiama Sandstone Member, or the Kiama Tuff. It is a prominent purplish, reddish sandstone up to 53 m thick, well exposed in road cuttings in the northern part of Kiama.

So, here we have the underlying sandstone deposited rapidly, not long before the thick lava was erupted, and that not long before the the overlying sandstone was deposited, all in the presence of abundant water. These three geological members could be described as contemporaneous with each other. Considering how quickly basaltic lava would crystalise in the presence of water, we are talking in terms of days or weeks at the most.

There is a time problem here but not for the biblical geologist. It is the uniformitarian geologists, who imagine these rocks formed over millions of years, who have the time problem. Where are they going to insert all those millions of years into these rocks?

10 Responses

  1. John Beasley
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    Tas, that’s great. Having lived in Wollongong and knowing the area well, it is a beautiful summary of the geology and all the better for being an explanation that fits in with the Biblical accounts of the flood and the immediate post-flood events.

  2. Peter Burger
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    Tas,
    From where were the sands derived? Was the source pre-existing sediments or primary (Creation Week) rocks?

  3. Tas Walker
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    Hi Peter, Conventional thinking is that the sediments of the Sydney Basin were derived from erosion of the Lachlan and New England Fold Belts, which I interpret as being deposited earlier in the Flood.

  4. Laurie Appleton
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    Hello Tas,

    Thanks for your message. I had not previously known that there was such a “blowhole” in that area, although I knew that there were such things somewhere. I imagined that there was one of perhaps more in West Australia in the Great Australian Bight. Is that correct? How many are there in Australia that we know of?

    Bless you and your work.

    Laurie.

  6. Tas Walker
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    Hi Laurie, A blowhole is just a crack or hole in the rocks that the waaves wash into and splash up. There is another one just a few kilimetres south and it is called the Little Blowhole.

  7. Carl Froede
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    Hi Tas:

    Thanks very much for the information.

    One point. You wrote:

    The volcanic flow sits on a formation called the Westley Park Sandstone Member, sometimes called the Westley Park Tuff because it contains lots of volcanic ash. This displays many sedimentary structures such as bedding, cross bedding and scour and fill—evidence of deposition from flowing water.

    COMMENT: All of these same sedimentary featues have been documented in subaerially deposited volcanic strata where no water was involved. You can expect the same for the subaqueous setting and gas transport would carry the materials away from the vent—not water. You do not need to invoke aqueous transport. Peperites are a welded mix of varying volcanic rock. That welding occurs in a HOT environment—again suggestive of volcanism (subaqueous?) and not aqueous transport.

  8. Andrew Rodenbeck
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    Some of the formations you describe appear to be a clear case of cold supersaturated plumes of sediment being misidentified as igneous rock. I think this will eventually be used as a critical indicator in correctly interpreting geology in the flood paradigm. At some point I would love to nail down experimentally the exact process to reproduce these unique features, but for now I’m stuck with merely envisioning a complex physical and chemical process that combines several different effects I have observed.

    Consider this. You say there is volcanic ash that

    “displays many sedimentary structures such as bedding, cross bedding and scour and fill—evidence of deposition from flowing water. The contact between the sandstone and the volcanic rock is highly irregular because the sediment and lava had mixed together.”

    Might you also describe this contact as interbedded? Are there cyclothems? These structures form by specific processes that require liquefied particles. Liquid rock can not make them because the particles act as a viscous liquid instead of sliding past each other as in a liquefied flow. The crossbeding in particular shows exactly the depth and direction of the flows and can be used to reconstruct the process in detail.

    Wouldn’t it be fascinating to make pepperite like that at Tennant Creek? I think I know how.

    The tricky part to combine a physical process that produces the large scale layering with chemistry that produces the large crystals.

    You write

    “When viewed on a geological map, it is clear that the porphyry sheet is conformable (parallel) with the strata of the enclosing sediments, the Warramunga Group. However, at closer range, when observed in outcrop, the contact between the porphyry and the sediment is highly irregular. At the upper contact there is an intricate penetration of the porphyry upwards into the overlying sedimentary host rocks and of the sediment downwards into the porphyry “

    and also

    “The intimate mixing of the two kinds of rock can be observed at a very fine scale. For example, wisps of sandstone only centimetres long are distributed irregularly in the porphyry and similar-sized quartz and feldspar crystals, edged with fine groundmass (from the porphyry), are ‘floating’ in the sandstone matrix. In fact, it is common for the clasts of each rock type to have a fluidal shape, suggesting that they were incorporated while they were still soft and fluid. Not only that, but close to the margin, the bedding in the fine sandstone and siltstone is rarely recognizable because it is so disturbed.”

    Because I have seen these effects in experiment your description immediately jumps out at me. This is what it looks like when you have parallel layers of sediment previously deposited disturbed by liquefaction shortly after they are formed. Plumes of sediment on a wide variety of scales intrude from lower into upper and upper into lower layers. These plumes take the shape of wispy fingers, pillars or towers, arches, bulges, or elongated bubbles of one material floating up or down into the opposing material.

    The trouble geologists always have in trying to interpret these things is the assumption of heat. This assumption naturally follows from the basic misidentification of the rock as igneous and is confirmed in the mind when the contacts surfaces are observed. I can see you followed the same reasoning.

    “the sedimentary rocks at the contact have been significantly hardened as a result of heating by the porphyry and break with a conchoidal fracture, like glass”

    . But the reason for the change in crystal structure at the contact is not melting. It is dissolution.

    You correctly reason that magma could not have slowly intruded, but then you make the inverse error and opt for rapid intrusion of magma. However that is also impossible. You write:

    “It does not appear that the intrusions were explosive or that fragmentation was caused by expansion of steam, which suggests the pressure due to the overlying water and sediment was great enough to inhibit steam generation. There was plenty of water to remove the heat so that the whole intrusion was cooled rapidly and the groundmass formed a microcrystalline texture—a coherent glass.”

    The trouble is the critical temperature for water is only 374 C, and quartz and feldspar melt at far over 1000 C. No amount of pressure would keep the water in the liquid phase. Also the “rapid” cooling of vast bodies of rock is impossible by any kind of heat transfer at their surface because the rock insulates itself. This is why, for instance there is still any liquid rock near the surface at all thousands of years after the flood. But in this case, and many others, the rock was not liquid or even hot.

    The secret is a proper understanding of concentration boundary layers. What does “saturated” mean? Saturation limits are determined experimentally for bulk fluids in quasi-static conditions. But it is not correct to apply such limits to a dynamic situation. Consider the concentration boundary layer: in a quasi-static experiment it is microscopic and consequently irrelevant. But, the concentration of a solute must approach that of the actual solid from which it is derived at the liquid/solid boundary. A concentration boundary layer develops the gradient from boundary conditions to free-stream conditions. However, in a dynamic situation it is possible for boundary layer conditions to extend into the bulk fluid some distance. Essentially the boundary layer becomes thicker. In the unique case of a liquefied flow the solid is dispersed throughout the fluid and it becomes possible that the boundary layers around each suspended particle interact to the point that bulk fluid properties are boundary layer properties. There is no free stream.

    This means, in the case of say liquefied quartz sand, that extremely high levels of dissolved quartz can be produced and maintained in low temperature water simply by agitation. Here is an experiment demonstrating this particular example.

    Ian Juby and I have observed the effects you describe using plumes of liquefied sediment intruding into sedimentary layers. However we haven’t yet put the chemistry and the fluid dynamics together in one experiment. I hope that flood geology will mature to the point where each and every rock we observe on earth’s surface can be experimentally reproduced in all aspects except for sheer scale.

  9. Say what?
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    “There is a time problem here but not for the biblical geologist. It is the uniformitarian geologists, who imagine these rocks formed over millions of years, who have the time problem.”

    Yea and the volcanoes from which the lava came from were also made in a matter of days right?

    Science and religion dont mix.

    Response from Tas Walker:
    Hi Say what?
    Yes, the lava from the volcanoes was erupted within days. See this report on the Columbia River Basalts for field evidence of very rapid lava emplacement.

  10. HeRrOgOoDbAi
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    Ummm just one rquest when were these rocks formed is it over millions of years ago or…?

    Tas Walker responds:
    These rocks were formed during the global Flood of Noah, as the waters were increasing on the earth.