Glass House Mountains Formation: Plate Tectonics Report

Scientific report

This report discusses varies types of theories and mainly focuses on the Glass House Mountains. There have been many theories that tried to explain why there are earthquakes, volcanoes, mountains and deep-sea trenches over the surface of the earth. Among all the theories, plate tectonics theory is most scientific and universally accepted. It is based on a broad synthesis of geologic and geophysical data. It deals with dynamics of Earth’s outer shell-the lithosphere that revolutionized Earth sciences by providing a uniform context for understanding mountain-building processes, volcanoes and earthquakes.( Tjeerd H. van Andel and J. Brendan Murphy, May 10, 2019 )

According to plate tectonics theory, Earth has a rigid outer layer, known as the lithosphere, which is typically about 100 km thick and overlies a plastic (moldable, partially molten) layer called the Asthenosphere. The lithosphere is broken up into seven very large continental and ocean-sized plates, six or seven medium-sized regional plates, and several small ones. These plates move relative to each other, typically at rates of 5-10 cm (2-4 inches) per year, and interact along with the boundaries where they converge, diverge or slip past one another. Such interactions are thought to be responsible for most of Earth’s seismic and volcanic activity, although earthquakes and volcanoes can occur in plate interiors. Plate motions cause mountains to rise where plates push together (or converge see figure 1), and continents to fracture and oceans to form where plates pull apart (or diverge). All the continents are embedded in the plates and drift passively with them, which over millions of years results in significant changes in Earth’s geography. Incorporating the much older idea of continental drift as well as the concept of sea floor spreading, the theory of plate tectonics has provided an overarching framework describing the past geography of continents and oceans.

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Plate Movement:

Plates on Earth’s surface move because of the intense heat in the core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools, and eventually sink down. As the cooled material sinks down, it is warmed and rises again. This process is known as convection currents. This process causes the tectonic plate to move. Scientists once thought that Earth’s plates just surfed on top of the mantle’s giant convection cells, but now scientists believe that plates help themselves move instead of just surfing along. Just like convection cells, plates have warmer, thinner parts that are more likely to rise, and colder, denser parts that are more likely to sink. (May 21, 2008 by Lisa Gardiner) (refer to figure 2)

Volcanoes are formed when one tectonic plate subducts underneath the other tectonic plate. Volcanoes are also formed when deep within the Earth is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and pushes through vents and fissures in the Earth’s surface. Magma that has erupted is called lava.

The Glass House Mountains formation:

Glass House Mountains are intrusive plugs. They are remnants of volcanic activity which occurred approximately 25-27 million years ago. Between 22-30 million years ago, south-east Queensland was rocked by prolonged volcanic activity that was caused by the continent moving over a hotspot in the Earth’s mantle (Mary Cairncross, 2019). As the Australian continent drifted due to convection currents (which is a process that moves tectonic plates) magma chamber from the hotspot created magma flows that filled the volcanic pipes. The process continued for about 25 million years until Australia completely moved out of the hotspot, resulting in causing the volcano to go extinct as the volcano had no lava flow. Molten rock filled small vents and solidified into denser rocks bring Trachyte and Rhyolite Queensland Government, Department of Environment and Science – 2019). The denser rock resisted erosion, while the softer rocks weathered away. This resulted in exposure of the dense rocks, now know as the Glass House Mountains.

Australia is on the Indo-Australian plate and is not located near a plate boundary and so earthquake activity is minimal unlike New Zealand. Australia witnessed volcanic eruptions several thousand years ago. About 22-30 million years ago, south east of Queensland was rocked by prolonged, volcanic activity. This was caused by the continent moving over a hot spot in the Earth’s mantle which is beneath the crust. (Sunshine Coast Council and 2018). Over the years, the continent drifted towards the south from the hot spot causing the lava flow to stop. Over the years the continents drifted due to the convection current theory as stated above. Which caused dome-like magma plugs to rise dramatically through the surrounding older rocks, filling volcanic vents or subsurface bulges. (Sunshine Coast Council and 2018) Throughout the years these subsurface bulges have cooled down to form the present-day Glass House Mountains.

The Glass House Mountains are now considered as extinct as they are intrusive volcanic plugs. The Glass House Mountains were originally basalt rock, but throughout the years the rock has been washed away due to weathering and erosion, leaving Rhyolite and Trachyte behind from the volcanic plugs.

In geology, hotspots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with surrounding mantle. Their position on Earth’s surface is independent of tectonic plate boundaries.

On Indo-Australian plate there are three hotspots. They are: Lord Howe, Tasmantid hotspot and East Australia hotpot. These are hotspots that were formed about 1000 years ago. As the Tectonic plate theory suggest that tectonic plates move, but hotspots stay in the same place. The East Australian hotspot is a volcanic hotspot that forces magma up at weak spots in the Indo-Australian plate to form volcanoes in Eastern Australia.

While Australia is home to the world’s longest chain of continental volcanoes stretching more than 2,000 km along the east coast, it is south-east Australia that features the country’s only active volcanoes. Mount Gambier’s Blue Lake and the nearby Mount Schank are Australia’s most recently active volcanoes, having erupted about 5,000 years ago. With an estimated eruption frequency of once every 10,000 years, the likelihood there will be activity anytime soon is not high. As per Monash University volcanology lecturer Jozua van Otterloo said another eruption was still expected — over the next 5,000 years. It is very hard to estimate when a eruption is going to be in south-east Australia because it’s such a large area. The last eruptions were Mount Gambier and Mount Schank, so we could expect another volcanic eruption in that area.( Kate Webber and Selina Green, 27th May, 2016)

Reference list

1. Kate Webber And Selina Green 2016, Volcanic eruption still possible in south-east Australia ... in 5,000 years or so, ABC, viewed 6 June 2019, < https://www.abc.net.au/news/2016-05-27/volcanic-eruption-still-possible-in-south-east-australia/7451878 >
2. Lisa Gardiner 2008, How Do Plates Move?, Windows2universe, viewed 6 June 2019, < https://www.windows2universe.org/earth/interior/how_plates_move.html >
3. Herb Kirchhoff 2018, What Are Convection Currents? Sciencing, viewed 6 June 2019, < https://sciencing.com/convection-currents-8172073. html >
4. Tjeerd H. Van Andel J. Brendan Murphy 2019, Plate tectonics, Encyclopædia Britannica. Inc, viewed 6 June 2019, < https://www.britannica.com/science/plate-tectonics /Development-of-tectonic-theory >
5. Bibliography
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7. Kate Webber And Selina Green 2016, Volcanic eruption still possible in south-east Australia ... in 5,000 years or so, ABC, viewed 6 June 2019, < https://www.abc.net.au/news/2016-05-27/volcanic-eruption-still-possible-in-south-east-australia/7451878 >
8. Herb Kirchhoff 2018, What Are Convection Currents? Sciencing, viewed 6 June 2019, < https://sciencing.com/convection-currents-8172073. html >
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10. Sunshine Coast Council 2018, Ancient Geology, viewed 6 June 2019, < https://www.mary-cairncross.com.au/glasshouse-moun tains-geology.php >
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13. What is a Hot Spot? 1971, Oregonstate, viewed 6 June 2019, < http://volcano.oregonstate.edu/what-is-a-hot-spot >