Geology

The Glasshouse Mountains are volcanic plugs that have been eroded over 25 million years during the Miocene period, to form 9 steep sided mountains.

What’s a volcanic plug?

Volcanic plugs, also know as a volcanic neck or lava neck, occurs when molten rock hardens in the vent of an active volcano.

How where they formed?

Once between 30-22 million years ago south-east Queensland had a lot of volcanic activity, many volcanoes were formed, and in turn were blocked with volcanic plugs. Then they have been eroded for about 25 million years, to make them look as they are today (steep sided mountains).

How are volcanoes formed?

Volcanoes are formed differently according to the type of volcano they are, one example is; when there is a gap between tectonic plates; this exposes lava which rises and as the lava cools it creates the ‘walls’ of the volcano.

What causes volcanic activity?

Volcanic activity is cause by ‘hot spots’ in the earths crust.

How old are the Glasshouse Mounatins?

The Glasshouse Mountains are approximately 25 million years old.

- Whats the Miocene period?

The Glasshouse Mountains were shaped during the Miocene period. The Miocene period meaning less recent is a period of time about 25 million years from the present.

What rocks are in them?

The Glasshouse Mountains are made up of two igneous rock types; Rhyolite and Trachyte.

Examples of other volcanic plugs-

The Glasshouse Mountains are only one example of volcanic plugs, there are many more volcanic plugs around the world, and here are some examples:

1. A volcanic plug in Rhumsiki, Far North Region, Cameroon.
2. The Edinburgh Castle in Scotland, built on top of an ancient volcanic plug.
3. The Ochoco National Forest of Oregon, USA’s volcanic plug.
4. The volcanic plug situated in Sri Lanka.
5. The volcanic plug in Saint Lucia.