The glasshouse mountains are volcanic peaks located in the Sunshine Coast, halfway between the hinterland and the coast. Unlike most volcanoes formed on plate boundaries, the mountains are bye-products of the East Australian hotspot. Hotspots are formed when anomalously hot magma, called thermal plumes, rise from Earth’s core into the mantle. Hotspots then develop on top of the plumes in the asthenosphere and melt the surrounding rock, creating a weak spot. The magma then rises through the cracks and erupts, producing volcanoes. As the magma heats up from the core, it begins to rise through the mantle becoming less dense. However, the further it travels, the more heat it loses to its surrounding, therefore, becoming denser again and sinking. This process repeats in a circular motion and the movement created is called convection currents. These currents are the reason plate tectonics move.
Plate tectonics is the theory that there are several pieces of solid rock in the lithosphere that move over the Earth’s surface and are the reason for its movement. As hotspots are stationary within the mantle, as a plate moves over it, a chain of volcanoes is created. However, as the plate and volcano move away from the hotspot, the magma cools and hardens becoming extinct.
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The East Australian hotspot cannot be seen, its exact location is unknown, but by analysing, the location of previous volcanic activity, the direction of plate movement, and past volcanic activity throughout eastern Australia a predication of its location can be made.
Approximately 31 million years ago, as Australia moved over the East Australian hotspot , a volcano south-west of Maleny was formed and began to erupt. The volcano remained active for around four million years and created numerous layers of basalt on the surrounding landscape from its eruptions. About five million years later, fissure vents were created underneath the basalt and filled with magma from the hotspot. The magma went through a chemical reaction and consequently, separated into Trachyte and Rhyolite. The magma then began to cool and harden, which created intrusive plugs within the vents. Millions of years later the basalt weathered and eroded, exposing the hard rock underneath it.
The theory of plate tectonics is what is currently acknowledged as the explanation for the movement and topography of Earth’s surface. This theory developed from Alfred Wegner’s proposal of continental drift, where he hypothesised that the Earth’s continents previously formed a supercontinent, called, Pangea. This land mass then broke into the seven continents and moved away from each other over geologic time. Wegner had compelling evidence supporting his claim, he studied both plant and animal fossils and found that some species were only found on the boarders of two continents. The species would not have been able to swim or migrate that far and the fossils found in some places were not adapted to survive in its climate. This suggests the area the fossils were in was once a different climate and location on earth. Furthermore, the continents were shaped as broken jigsaw pieces and look as if they were once one land mass that had drifted away from each other over time.
Moreover, Wegner discovered that the stratigraphy of the surrounding mountains and rocks on the boarders of continents matched. This indicates that the landforms were once connected. Wegner looked at the glacial deposits that formed when Pangea existed and discovered that the scratches on the bedrock from ice glaciers lined up with surrounding continents, proving they did come from a single central point.
Despite Wegner’s convincing evidence of this theory, it was discarded by scientist at the time for the lack of reason provided as to how the continents moved. Instead, it was a common belief that there were land bridges created from marine regression that connected the continents and allowed animals to migrate over. However, because of advancing technology, Wegner’s theory of continental drift was subsumed into the theory of plate tectonics and is now the widespread belief.
Along the east coast of Australia there is a mountainous region of around 1000km, ranging from, North Queensland to Tasmania, created from the East Australian hotspot. The hotspot is not currently expressing any volcanic activity, however, by analysing its past eruptions and direction of plate movement the location can be predicted. The chains of volcano are in chronological order, decreasing in age further south of Australia. The red dots move in a straight light with a slight curve near the bottom, indicating a change in plate movement. Based on this information, it can be presumed that the plate is moving north-east.
Using this knowledge, it is predicted the hotspot is found on the south-west coast of Tasmania. This is apparent since the plate has changed direction and created a curved chain of volcanoes. As the plate continues to move in a constant trend, which is proven from the most recent volcanic activity , it is determined the hotspot is off the south-west coast of Tasmania.
The East Australian hotspot is deemed to be in north-west Australia and presently does not display signs of volcanic activity. However, in the distant future, as the Indo-Australian plate continues to move, along two converging boundaries, the plate will subduct, creating volcanoes. Subsequently, the convection currents will cause the tectonic plates to change direction and move towards each other forming a future Pangea. Moreover, as this process happens over the span of billions of years , the plate will potentially travel over other hotspots and develop new boundaries, generating volcanic activity throughout the continent. The Indo-Australian plate could theoretically also become part of the Ring of Fire, where there is an abundance of frequent activity. However, this activity will not occur for millions of years. Furthermore, the Australian continent will have future volcanic activity, but it might not be correlated to the East Australia hotspot for several years.
Examining the glasshouse mountains gives insightful information into the location of the East Australian hotspot. By analysing the direction the Indo-Australian plate is travelling, examining the pattern of previous volcanic activity, and using the theory of plate tectonics an accurate estimation of the hotspot is made. By evaluating this information, it is justified that the Australian continent will experience changes in volcanic activity in the future.
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