Tertiary Volcanoes

The processes responsible for plate tectonics and the movement of continents occasionally result in the formation of some oddities.  Hot-spots can persist within the earth creating volcanoes in areas that they would not otherwise be expected. A modern example is the islands of Hawaii which are forming as the Pacific plate slowly moves across a hot spot in the earth. Between 30 and 20 million years ago southern Tasmania was host to many small volcanoes.  Often occurring near river valleys or old fault lines, they erupted basaltic lavas and ash.  Dark black, bubble-filled basalts can still be found in areas around Hobart today.
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Around 25 million years ago volcanoes producing basaltic ash and lavas were common around the Hobart area.  Rocks formed by these processes include bubble-filled basalt (right) from Margate, Tasmania.