Shaping the Landscape

The mountains east of Melbourne have been built by a series of geological events and shaped by a long, continuing process of erosion from water.

There are five clear phases in this process from 500 million years ago until today.

1. Assembly phase 500 - 370 million years ago
2. Glaciation phase 290 - 270 million years ago
3. Mountain-building phase 250 - 200 million years ago
4. Breaking-up phase 100 - 70 million years ago
5. Today's mountain catchments 0 million years ago

Phase 1 Assembly

Continents collide creating rugged mountains Source - NASA

The eastern part of the Australian continent didn't exist at all at around 500 million years ago. From about this time through to 370 million years ago (a period of some 130 million years) eastern Australia was assembled from a number of continental fragments that arrived from the east (driven by plate tectonic processes, ie. continental drift) and collided with the existing crust. The continent-continent collisions folded and distorted the crust along the line of collision, creating rugged mountains. Land slides, scree and boulder strewn valleys would have been common. Some of the crust that was pushed downwards by this collision reached temperatures sufficient to melt the rocks. The molten material (magma) was pushed into the deformed sedimentary rocks where it cooled and crystallised to form granite.

Phase 2 Glaciation

Glaciers carve out U-shaped valleys Photographer - Luke Simpkin Source - Museum Victoria

During the Permian (290 - 270 million years ago) Gondwana (of which Australia was a part) was located close to the south pole. Because of its polar location Australia was partly covered by a major ice-sheet at this time (similar in size to the present East Antarctic ice-sheet). As Gondwana moved northwards to lower latitudes the ice-sheet would have melted and the final phase of the glacial activity would have been mountain glaciers within the highland region of eastern Australia (similar to the present mountain glaciers in the Southern Alps of New Zealand). These mountain or valley glaciers scoured steep U-shaped valleys through the mountainous topography.