Origin of Black Mountain, North Queensland, Australia
As you first approach Black Mountain, 25 km south-west of Cooktown in North Queensland, it looks like it has been burned in a bushfire. However, the dark colour comes from the immense jumbled pile of black, blocky boulders, some as big as houses, that cover the whole mountain (figure 1). The intact solid granite core is said to lie beneath the jumbled broken blocks. The boulder fields of Black Mountain National Park form an impressive and distinctive landscape of international geological significance.
The large outcrop of granite that forms the mountain was emplaced deep beneath the surface of the earth as an enormous pool of molten magma, called a pluton. This happened some 4,500 years ago during Noah’s Flood, several months into that catastrophe as the floodwaters were rising. The magma was pushed into place through fissures in the earth’s crust as tectonic forces moved and cracked the crust. The kilometres of rock material above the granite was greatly eroded later during Noah’s Flood by the powerful movement of floodwater, with the most recent period of erosion occurring as the waters were receding from the continent into the present ocean basins. After the overlying rock was removed and the granite was exposed at the surface it cracked into blocks, which now loosely cover the original granite mountain.
The granite has been named Trevethan Granodiorite. It is not black but a light colour, mainly white to grey, and composed of minerals such as feldspar, mica and hornblende.1 The boulders are hard and blackened by a film of microscopic blue-green algae growing on their surfaces. It is this organic film that gives the mountain its distinct black colour and is the origin of its name—Black Mountain.
The granite was likely first broken into blocks as the kilometres of overlying rock was removed from above. This would have released the enormous overburden pressure pushing down on the granite allowing the granite pluton to expand and crack into blocks along lines of weakness at its surface. These fractures, called joints, can run parallel or slightly curved to the surface of the granite monolith. This cracking can loosen sheets of rock that can be tens of meters thick, resembling huge onion layers called exfoliation joints.
Grey patches on the mountain and on boulder fractures indicate that rock disintegration is ongoing. Some have suggested the process is accelerated dramatically when very hot rock heated by the sun is suddenly quenched by cold rain, sometimes with explosive results. Some have said that the occasional loud cracks heard at the mountain are blocks suddenly fracturing. All this means that the initial formation of the blocks occurred very late in the Flood as the waters were receding. It had to be late in the Flood after most of the strong currents of water had abated or the blocks would have been washed off the surface. Ongoing block formation has continued in the 4,500 years since the Flood ended.
In more detail
This is the story about Black Mountain in summary form. For more detail about its formation consult this article about the geological history of the Brisbane area. Although this article describes what happened around Brisbane it is also relevant to the area around Cooktown. In fact, the same general story applies to the whole of eastern Australia.
As you read the article about the Brisbane area, note that first sediment and volcanic material was deposited as the floodwaters were rising (see figure 2 adapted here from that article). In the area around Cooktown some of these early-Flood rocks have been called the Hodgkinson Formation. Secular geologists say this happened some 360 million years ago, but it was actually about 4,500 years ago in the first half of Noah’s Flood as the waters were rising, possibly just a few months after the year-long Flood began.
We can dismiss the million-year dates published by mainstream geologists because these are simply assumptions. They have chosen dating methods and interpretations so that they can obtain a logical timing sequence. Always their numbers are constrained by the evidence in the field, and they have no qualms about rejecting dates that do not fit with the other evidence and their philosophy. We work the same way but constrain our dates by the real history of the world documented in the Bible. For more on the issue of dating see How dating methods work, Radioactive dating anomalies, and The dating game.
Then, as the Flood continued, the crust of the earth heaved catastrophically, folding, pushing, uplifting, and metamorphosing these rocks. The area of folded rocks has been called the Hodgkinson Fold Belt (figure 2). This enormous crustal movement also melted rocks deep in the crust producing magma (liquid rock) which squeezed through the crust, pooled under the surface of the earth, and would also have erupted on the surface kilometres above. This is the origin and timing of the granite that formed Black Mountain. Secular geologists say this folding happened some 250 million years ago, but it was in the first half of Noah’s Flood as the waters were rising, perhaps a few weeks after the sediments had been deposited.
Granite has long been considered a problem for the Flood interpretation because it has been claimed that it takes far too long to form within the biblical timeframe. However, this problem has evaporated in recent years as more research into granites has confirmed they can form quickly. For more information see Granite formation: catastrophic in its suddenness, and Granite grain size not a problem for the rapid cooling of plutons.
As the Flood continued, more sediment was deposited over Australia including the sediments of the Sydney, Cooper, Galilee, and Bowen basins (figure 3), and then the vast area of sediments containing the Great Artesian Basin (figure 4), in which are found dinosaur fossils, including dinosaur footprints. It is highly likely that this sediment would have extended to the Cooktown area and covered the Black Mountain pluton.
After the Flood peaked, the ocean basins started to sink, and the floodwaters began to run off the continent into the ocean. This process took more than six months. As the waters flowed off, they eroded kilometres depth of material from the surface, exposing rocks that had previously been deeply buried. This erosion uncovered the granite intrusions around Cooktown and Townsville, including Black Mountain. You can see on figure 4 how that the yellow sediments do not extend to the Townsville and Cooktown area. These sediments would have been eroded away as the floodwaters were receding off the continent.
It was very late in the Flood and afterwards that the mountain broke into the huge blocks that now cover the pluton that forms its core.
When we understand the big picture of the Flood, we can easily re-interpret individual geographic features within a biblical perspective. It is important to be able to do this. People and institutions that reject the Bible as it is written, particularly its account of Noah’s Flood, are continually presenting explanations of landscape features in terms of millions of years, which is a return to the old Greek way of looking at things. The wholesale promotion of this philosophy is affecting our whole culture, which was built on the biblical foundation with God as Creator. This constant repetition of evolutionary thinking is leading people to think the Bible has no relevance to the real world, and to lose their way. By reinterpreting geologic information like this for significant sites we can help strengthen faith and keep people on the true path.
References and notes
- The granite was originally named Trevethan Granite. It is described as mainly white to grey, medium-grained, porphyritic, (orthopyroxene-) (clinopyroxene-) (hornblende-) biotite monzogranite and granodiorite, with scattered mafic and gneissic enclaves. Return to text.