Logging Tasks:
1 In your own words, describe how scoria cones form.
2 Give two examples of volcanoes that exhibit the characteristics of scoria cones.
3 Around the periphery of the Scoria Cone Picnic Area, you will find examples of scoria. Select a piece of scoria and describe what you see.Please do not take this sample home with you.
4 Please include a photo of yourself, your team OR an identifiable object showing the pavilion/visitor centre with your log.
Feel free to log your find straight away but message the question answers to the cache owner within two weeks of your find. Logs without an acompanying photo or without answers being sent may be deleted without notice.
The Lesson
Scoria cones, also known as cinder cones, are relatively small, steep-sided volcanoes built from loose pyroclastic fragments, mainly scoria, that are ejected during explosive eruptions. They are the most common type of volcano and are characterized by their conical shape and a bowl-shaped crater at the summit.
The Organ Pipes National Park car park and picnic area are situated on the remnants of a weathered scoria cone. Around 800,000 to a million years ago, while larger volcanoes to the north were producing lava, this cone erupted, ejecting molten rock and creating scoria. Scoria is a brownish, lightweight rock with air pockets, formed when steam escapes during volcanic eruptions.
Here is a more detailed look at scoria cones and scoria:
Formation:
Scoria cones form when gas-charged lava is blown violently into the air, breaking into fragments (cinders, clinkers, or scoria) that solidify and fall around the volcanic vent. These fragments accumulate, creating the cone shape with slopes typically between 30° and 40°.
The loose, unconsolidated material of the cone usually prevents lava from erupting from the top, so lava flows often breach the side (a local example of this is Mt Franklin near Daylesford) or emerge from a flank vent.
Characteristics:
Size:
Scoria cones are relatively small, ranging from tens to hundreds of meters in height.
Shape:
They are characterized by their steep usually 30-40 degrees, conical form and a crater at the summit.
Composition:
Scoria cones are composed of basaltic or andesitic lava fragments, which are typically vesicular (containing gas bubbles).
Location:
They can occur as individual volcanoes or on the flanks of larger volcanoes like shield volcanoes, stratovolcanoes, and calderas. An example of this is Mauna Kea in Hawaii, which has many scoria cones on its flanks.
The scoria cone is located within the Organ Pipes National Park, near the car park, and is part of the broader volcanic landscape of western Victoria.
Eruptions:
Scoria cones often form during relatively short-lived eruptions, sometimes lasting for just a few days or years.
Hazards:
Scoria cones can pose hazards from lava flows, ballistic ejecta (flying rocks), and volcanic ash.
Scoria Formation:
The scoria was created when molten rock, or lava, was ejected from the volcano in a series of explosive eruptions.
Air Pockets:
The scoria contains numerous air pockets, giving it a lightweight and porous texture.
Color:
The scoria is typically a brownish color.
Many scoria cones in Australia are located in the Newer Volcanics Province in Victoria and South Australia.
Some notable scoria cones in Australia include:
- Mount Franklin (Victoria) A breached scoria cone.
- Mount Elephant (Victoria): Described as a steep-sided volcanic scoria cone and one of the most prominent volcanoes in Australia's Western District.
- Mount Noorat (Victoria): An impressive scoria cone with multiple eruption points and a large, deep central crater.
- Mount Warrenheip (Victoria): A prominent scoria cone just east of Ballarat.
- Mount Fraser (Victoria): Located near Beveridge, north of Melbourne.
- Mount Napier (Victoria): Features a breached scoria cone superimposed on a lava shield.
- Mount Sugarloaf (Victoria, near Mount Leura): A classic conical accumulation of scoria.
- Mount Fox (Queensland): Although Queensland's Mount Scoria is not actually a scoria cone (it's a basalt lava plug), Mount Fox is an example of a scoria cone in Queensland.
Scoria cones are conical hills built up around a volcanic vent, composed mainly of scoria (a vesicular, dark-coloured volcanic rock) which forms when gaseous blobs of lava are ejected from the volcano.
Glossary
Andesitic - meaning relating to or containing andesite, a gray, fine-grained volcanic rock.
Pyroclastic - describes volcanic rock fragments, materials, or deposits formed by explosive volcanic eruptions.