Geology and soils

Geology, as most people know, is the study of rocks. This is relevant for many fields, including

  • Mining – to be able to find, map and extract minerals that society need to function;
  • Archaeology – to reconstruct the type of environments that existed in the past;
  • History – the rocks of the area may influence everything from where to build a city and what to build it from, to wars over mineral resources, to the success of agriculture due to the nature of the soils;
  • Botany – plants have evolved to prefer different types of drainage and soil nutrients, which is related to the rocks from which the soil is derived;
  • Soil Science – the type of soil, drainage and nutrient level is dependent on the rock type;
  • Engineering – buildings and bridges for example need a strong foundation which may vary with the rock type.
  • Hydrogeology – the study of groundwater in rocks, where different rock types have more or less water than others. This affects water supplies in many parts of the world.

The present day landscape and soils are a result of past events. For instance, Victoria has gone through volcanic eruptions, sea level changes and erosion to become the soils and landscape of the present day. The diagram below outlines past events.

vic geology

 

The area of Berwick mainly comprises four different rock types.

  • Lower unit (bedrock) of siltstone, which was once soft muds on the ocean floor
  • Volcanics such as basalt flows from volcanoes, mixed with cooked sediments, ie Wilson Park quarry
  • Recent sand and clay sediments from river erosion
  • Granites, found further north and west.

The map below shows where these rock types occur.

berwick geology

Soils

Soils differ according to the rock below. One exception to this is a secondary soil that has been moved to the area as a result of river flooding and the like. Weather also affects the soil profile. Australian has the most nutrient poor soils due to extensive weathering of very old rock, such as that found in WA and in desert regions. In Victoria we are luckier n that the more recent basalt lava flows during the Cretaceous has resulted in fresher, more nutrient rich soils.

Basalt is a heavy black rock that weathers to a rich orange brown heavy clay with poor water drainage. In the area it is quite close to the surface, depending on the topography. Wilson Botanic Park was a basalt quarry.

Siltstones weather to a silty greyish soil that is prone to having water repelling properties. It is relatively poor in nutrients.

Sandstones and gravels vary depending on the clay content, with pockets of clay rich poor drainage possible next to fast draining sands.

Granites weather slowly, often outcropping at the surface. Soils are sandy, well drained and low in nutrients.

All of these soils will have different indigenous plant communities that have adapted to the soil type. It is well worth paying attention to your soil so you can adapt your garden to the soil. It will be many years of labour to significantly change a soil, or expensive to import topsoil. Plants that are suited to the soil type will also do better with variations in rainfall and dryness.

The road cuttings below show some of the rock types and soils found in the Berwick area, along Kangan Drive, although these are covered in now.

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