Volcanic caves of Victoria (Small Tubes)

Subcrustal caves

Small, shallow, subcrustal caves form near the surface of a lava flow by drainage of still-liquid lava from beneath a thin crust.

See also
Poster (PDF) on Formation of Lava Caves by various processes (KG Grimes, 2010). Prepared for the International Symposium on Volcanospeleology, Australia, August 2010. Paper (PDF) on Subcrustal Lava Caves (Victorian examples): KG Grimes, 2008, in Espinasa-Perena R & Pint, J (eds) Proceedings of the X, XI and XII International Symposia on Vulcanospeleology, Association of Mexican Cave Studies, Bulletin 19: 35-44. (2008)
Field Guide (PDF) to the Volcanic Caves of Western Victoria: KG Grimes (ed), 2010, Prepared for the 14th International Symposium on Volcanospeleology, August 2010.

Selected photographs and diagrams

To view full size images, click on the displayed image.
Small is better!
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Proto-tubes

These are the first-formed tubes, which conduct lava through a set of small but discreet lava lobes. Over time most of them stagnate but a few capture the bulk of the flow and grow larger. Where a large tube intersects an earlier proto-tube the latter may partly drain along with the bigger tube so we can see it.
A pair of Proto-tubes in the ceiling of a larger tube at Mt. Hamilton Cave.
10 cm scale bar.
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A group of proto-tubes in the upper-level passage of Mt. Widderin cave, Skipton.
Stereopair, view cross-eyed. 10 cm scale bar.
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A very small proto-tube. Note the mounded lava surface above (yellow dashed line) and stretched vesicles, which suggest inflation above the small tube.
In the wall of the sinkhole above Harman 1 cave (3H-11), Byaduk.
10 cm scale bar. KG100560T.JPG

Lava Blisters, and other small cavities

Maps of some small subcrustal chambers. These are the simplest forms we find.
"Lava Blister". A small subcrustal chamber beneath a low mound on the lava surface.
Turtle Cave (3H-90), Byaduk
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The small chamber, with lava drips, of Turtle Cave (3H-90), Byaduk.
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A shallow tube, showing the thin roof. 3H-64, Mt Napier.
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Part of the upper-level crawls above Fern Cave.
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Not all tubes drain at the end of the eruption!
A completly lava-filled tube is exposed by breakdown at the edge of a lava channel at Mt Eccles. IMG00018.jpg

A set of three stacked subcrustal caves

For more details see the descriptions and maps of two of the caves imaged below 3H-106 and 3H-108 at Byaduk. These two and H-74 form a stack of three caves in separate thin lava flows.
A set of slightly more complex subcrustal caves. These have multiple chambers, and they have formed as a set of three, each in its own separate lava flow.
View of the entrances (numbered) to the three separate levels of caves. The cliff is the wall of a collapse into a deeper major feeder tube.
Chamber in 3H-74. Note sags and bulges in ceiling.
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Small chamber in 3H-74, with pahoehoe lava floor and lava drips on ceiling.
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A typical small low chamber in a subcrustal cave. 3H-106.
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Evolution into small feeder tubes

Continuing flow through a subcrustal system enlarges the active parts and modifies them into large and more cylindrical shapes.
These can act as feeder tubes for the advancing flow-front.
See also the Mt Hamilton Lava Cave, which has even larger evolved tubes, with remnants of the original tubelets in its walls.

A small feeder tube at the start of 3H-53, Mt. Eccles
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Another small cylindrical tube (3H-87), Mt. Eccles
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