Mount Watch is a scoria dome volcano and forms a subsidiary vent to The Bluff volcanic system. Most of Mount Watch is blanketed by a thick, consolidated sand sequence. The quarry on the peak of the mountain gives access to the underlying scoria. Mount Burr Range contains 15 volcanic eruption points. The Mt Burr Range volcanics are much older than Mt Gambier and Mt Schank, and date from 20,000 to two million years old. During eruptions, the Pleistocene sea was lapping at the base of the structure, causing erosion by waves and onshore winds. There are sedmentary structures on the western flanks that have been produced by coastal processes.
Scoria cones are the commonest type of volcano and are also the smallest type, with modest heights of generally less than 300 metres. Scoria cones are composed almost wholly of basaltic tephra, ejected from lava fountains, or mildly explosive eruptions from a single vent which shoots melted rock fragments into the air. These cool rapidly as they pass through the air and fall back to earth, landing around the vent and accumulating in the typical cone shape.
Scoria rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. Scoria is actually a kind of glass and not a mixture of minerals. A reddish, poorly developed soil that formed on a basalt deposit associated with the extinct volcano Mt. Watch near Millicent, has a mineral composition that consists predominantly of pyroxene, smectitie,illite, and halloysite. The presence of the mineral halloysite is indicative of soils of basaltic origins (Hosking et al., 1957), as are pyroxene andolivine.
At the listed coordinates you will see a cut face in the quarry. Please examine the cut face and prepare answers for the following questions. You can log a find immediately if you wish, however also send your answers within a reasonable period to confirm your understanding of the earthscience lesson.
-Estimate the general size of the scoria. Would you describe the mineral as sand, gravel or rock?
-Do you see any larger fragments on the cut face? What is the cause of these fragments?