The Lava Tubes of Budj Bim EarthCache

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Hidden : 2/15/2010
Difficulty:
4 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:



BUDJ BIM

bucketeer's 13th cache

Mt Eccles Volcano

The Mount Eccles volcano is believed to be formed by a relatively rare fissure type eruption, active between 33000 to 6000 years ago.
Early eruptions from the site are thought be have been of the 'Hawaiian type' with basaltic lava flowing freely from a central crater containing a lava lake.
A broad lava shield has been built up by successive flows of very fluid basaltic lava spread out from the central crater. A line of small scoria cones running southeast from the main crater were probably formed along the fissure, with the 3 largest craters joining to form the 700 metres long, spring fed Lake Surprise, at the centre of Mt Eccles. Late eruptions produced fountains of lava jetting skyward forming the scoria cones of Mt Eccles. 

Lava Flows and the Formation of Lava Tubes

Basaltic lava is hot at around 1100°C and flows readily. There are two main forms of basaltic lava flow, Pahoehoe and ?A?a which grade into each other. 
Pahoehoe lava is the most liquid form - characterised by the formation of thin smooth skins that become wrinkled. Pahoehoe lavas advance as a succession of lobes, each of which develops a skin, which is inflated by the liquid pressure within, and then ruptures at one or more points to release liquid lava to form new lobes.
As pahoehoe loses gas and cools it becomes frothy and stiffer. The surface tends to crack, twist and break into angular, often spiny, blocks to form what is called ?A?a or 'blocky' lava.
Behind the advancing lava front, stagnant areas solidify restricting lava movements to narrow surface channels, or tubes beneath a surface crust.

Overflow from the surface channels builds up a levee bank of thin sheets or spatter. Larger flows across a levee can feed lateral lava lobes with small internal lava tubes. A major breach of a levee may result in a large side flow, fed by its own channel, and the original channel may be abandoned. Good examples of lava channels or canals occur at Mount Eccles and a number of shallow lava tubes have formed in flows that have run off the sides from these channels. Lava canals exiting from the northern end of the Mt Eccles' main crater are 30-40 meters wide and 8-12 metres deep.

Lava tubes are formed by two main processes; first by the roofing over of surface lava channels in one of several ways; and second by the draining of still molten material from beneath the solidified crust of a flow.
Tubes formed by draining of crusted lava lobes and flows are generally smaller than those formed by the roofing of a channel, but tend to have more complex forms.

                
Maze Cave, 3 Dimesional Tubes Footes Cave, ?A?a Lava Flow on Left
   

Lava lobes can be stacked vertically as well as advancing forwards so that a complex three-dimensional pattern of inter-branching tubes can form. Lava tubes provide good insulation for the hot lava flowing within them. This allows the formation of very long flows such as the 50km flow from Mount Eccles to the coast at Tyrendarra.

Formation of Volcanic Caves

Volcanic caves are formed when, at the end of an eruption lava is drained away from a lava tube leaving only the shell or hollow tube. The level of lava within the lava tube fluctuates during the course of an eruption, and so thin linings plastered onto the walls and roofs, and 'tide-marks' indicated by solidified benches or shelves on the sides of the tube. The thin wall linings can rupture, peel back and curve over to form draperies and scrolls. Some linings are smooth, but others have a sharp hackly surface which may be due to the bursting of many small gas bubbles. Rafted slabs of solidified lava, floating on a flow surface may leave grooves on the semi-solid wall linings. Small round-tipped lava stalactites, (lavacicles, lava drips) form where molten lava has dripped from the roof.

Carmichael's Cave, Lavicles Smoko Cave, Cracking on Roof Smoko Cave, Tree Roots
                          

Lava ribs form where lava has dribbled down the walls of the cave, or where the whole lining has sagged and wrinkled. If the floor was already solid (which is unusual), drips of lava from the ceiling can build up lava stalagmites.
 
The floor of the tube is often flat or slightly arched, being the surface of the last flow of lava through it. If a lava flow within a tube forms a solid crust, and then drains away from beneath it, we get a tube-in-tube effect with a thin false-floor bridging the tunnel. Small lava mounds, or tumuli, may be heaved up by pressure from below. In some caves the crusted floor has buckled and broken into a jumble of heaved up plates, or cracked into a mosaic of jostling plates with rounded or upturned edges. Material falling from the roof may be rafted some distance downstream and may end up welded into the floor, or piled up in 'logjams'.

Tunnel Cave

Tunnel Cave is in the side of the main canal near the main crater of Mount Eccles.
Initially it would have been an open channel diverging from the main one, but the surface of the lava flowing in the channel cooled and solidified to form a crust. Additional lava overflows from the main canal buried this crust with a stack of thin layers, now visible in the cliff above the cave entrance. Molten lava continued to flow in the tunnel left beneath the crust and, at the end of the eruption, that liquid partly drained away to leave the cave we now see. The original large entrance has collapsed leaving the present entrance as a small hole left at the top of the large mound of collapsed rubble.

The Cave Environment
One would expect bats in a cave of this shape and size, but they are seldom seen now. The constant visitors disturbs their sleep and so they have taken to using other, more peaceful, caves. Bats are a major source of food in caves - they feed outside, but return to roost in the cave where their droppings provide food for a wide range of fungi, insects and other small animals. The departure of the bats and the trampling of the floor sediments by human visitors over the last 100 years means that there is little animal life here now.

Features of the Cave.
The arched roof and flat floor, resembling a railway tunnel, is typical of lava tubes. The original cross-section would have been elliptical, with the flat floor being created by the final stream of molten lava which solidified in the cave. Much of the roof has a jagged appearance suggesting that fragments have fallen away. The rubble pile at the entrance was formed in this way.
Along the wall to your left is a low bench; a 'tide-mark' left when the lava surface was slightly higher. Where the lava touched the wall it cooled and formed a semi-solid lining that can be anything from an inch to a foot or more thick.When the level dropped, the solidified lining remained to form a bench.
During much of the eruption the tube would have been completely filled with flowing lava. Towards the end, as the levels dropped, soft lava coatings a few inches thick were left on the walls and roof. The surface may have an irregular lumpy form, or have dribbles and drips, and horizontal or vertical grooves and ridges.  The horizontal lines are probably 'tide-marks', but the origin of the vertical marks is less certain and are possibly fragments of soft lining slid down the wall to leave grooves and ridges. In a few places one can see striated scrape marks left by fragments of crust that were floating on the surface of the lava river.
In places you see small flaps of lining that have broken free and sagged down, some of these appear to have burst like bubbles caused from gas pressure built up behind them.
 The original wall features are often hidden by a younger growth of knobby to prickly 'cave coral'. This is a mineral growth (mainly calcite) which has precipitated from water on the cave surface. The water picked up this mineral material from the weathered rock as it seeped down from the surface.
At the far end of the cave the roof drops and finally meets the floor, which is the surface of the undrained part of the underground lava flow that solidified in place and now blocks the remainder of the original tube. That tube, filled with liquid lava, would once have continued for quite a distance beyond. Note the wrinkles of 'ropy lava' on the floor here. These are small pressure ridges formed by the movement of a lava with a thick consistency.

Cultural Heritage and the Budj Bim National Heritage Landscape

Sacred to the Gunditjmara people, the Budj Bim National Heritage Landscape is home to the remains of potentially one of Australia’s largest aquaculture systems.
For thousands of years the Gunditjmara people flourished through their ingenious methods of channelling water flows and systematically harvesting eels to ensure a year round supply.  Here the Gunditjmara lived in permanent settlements, dispelling the myth that Australia’s Indigenous peoples were all nomadic.
Dating back thousands of years, the area shows evidence of a large, settled Aboriginal community systematically farming and smoking eels for food and trade in what is considered to be one of Australia’s earliest and largest aquaculture ventures.
This complex enterprise took place in a landscape carved by natural forces and are full of meaning to the Gunditjmara people.
More than 30 000 years ago the Gunditjmara witnessed an important creation being reveal himself in the landscape.  Budj Bim (known today as Mount Eccles) is the source of the Tyrendarra lava flow, which as it flowed to the sea changed the drainage pattern in this part of western Victoria, creating large wetlands.
The Gunditjmara people developed this landscape by engineering channels to bring water and young eels from Darlots Creek to low lying areas.  They created ponds and wetlands linked by channels containing weirs.  Woven baskets were placed in the weir to harvest mature eels.
These engineered wetlands provided the economic basis for the development of a settled society with villages of stone huts, built using stones from the lava flow.  Early European accounts of Gunditjmara describe how they were ruled by hereditary chiefs.
With European settlement in the area in the 1830s came conflict.  Gunditjmara fought for their land during the Eumeralla wars, which lasted more than 20 years.
As this conflict drew to an end in the 1860s, many Aboriginal people were displaced and the Victorian government began to develop resources to house them.
Some Aboriginal people refused to move from their ancestral land and eventually the government agreed to build a mission at Lake Condah, close to some of the eels traps and within sight of Budj Bim.
The mission was officially closed in 1919 with the Lake Condah Aboriginal Church was demolished by authorities in 1957.  The Gunditjmara continued to live in the area and protect their heritage and identity to see their Mission lands returned in 1987.
In 2007, the Gunditjmara achieved their recognition of their heritage and identity through the Federal Court of Australia’s Gunditjmara Native Title Consent Determination.  In 2008, Lake Condah was formally returned to Gunditjmara people by the State of Victoria.
The Gunditjmara manage the Indigenous values of the Budj Bim National Heritage Landscape through the Gunditj Mirring Traditional Owners and Winda Mara organisations.  A large part of the area is the Mount Eccles National Park which is cooperatively managed by the Gunditjmara and Parks Victoria.
The Budj Bim National Heritage Landscape was declared by the Australian Government in July 2004 for the following outstanding national  values:
·         the place has outstanding heritage value to the nation because of the place's importance in the course, or pattern, of Australia's natural or cultural history.
·         the place has outstanding heritage value to the nation because of the places' possession of uncommon, rare or endangered aspects of Australia's natural or cultural history.
·         the place has outstanding heritage value to the nation because of the place's importance in demonstrating a high degree of creative or technical achievement at a particular period.
·         the place has outstanding heritage value to the nation because of the place's importance as part of Indigenous tradition.

Mount Eccles National Park

Mount Eccles National Park is 6120 ha, which covers the majority of the lava flow from Mount Eccles.
Much of it is very rocky and difficult to traverse, but areas around the peak have good family friendly amenities, wheelchair accessible tracks, BBQs, picnic tables, and shelters.
If you're considering staying a little longer there's a campground second to none with flushing toilets and hot showers. (fees apply)
There are several interesting walks although some are little rough going, and not suitable for small children. I recommend the lava canal walk. The lake circuit & crater rim walks are also definately worthwhile.
There are numerous "wild" lava tube caves in the park (the above photos were taken in some of them), and you may see some on the lava canal walk.
The Park has a large koala population and sightings are not unusual.
A link to the Parks Victoria web site can be found here

Logging a Find on this Earth Cache

To log a find on this earth cache you will need to visit Tunnel Cave with a good torch and a digital camera with a flash.
Email me your answers to the following questions:
A) At the entrance to to cave is a small round metal disc with an alpha numeric code stamped into it. This code is used to uniquely identify this cave. As a sharp eyed geocacher you should easily find it. Record this number, and email me as proof of your visit. 
B) Towards the end of the cave (just beyond the low-roofed section with a waist high entry) look at the right hand roof at eye height. A cavity, large enough to fit your head into, has formed behind a span of lining that broke free and sagged into the empty cave while still soft. Look into this cavity and find the VOLCANIC FEATURE that lies within it (HINT: It's not the small stalactite). It may pay to take a photograph if you're not sure so you can analyse it at home. Email me your description of what lies within this cavity.
C) Find the lava bench within the cave, as described above and estimate it's height. Email me your answer.

Do not post answers or photos of any of the above features with your log.

D) Take a photo of yourself or your GPS (or you and your GPS) either inside the cave, at the entrance to the cave (with the entrance clearly visible) or at the nearby Lake Surprise lookout (with the lake clearly visible), and post it with your log. Please describe your visit to Mount Eccles & what you most enjoyed in your log.

Any logs that do not meet the above requirements will be deleted

I hope you enjoy your visit.



Acknowledgements
Thanks to the Victorian Scout Caving Team for introducing me to many of the caves at Mt Eccles and rekindling my interest in caving.
Thanks also to the Gunditjmara People, the Budj Bim Council, and Peter Hill from Parks Victoria, for approving  the placement of this earthcache and providing the cultural heritage notes

References
Birch, William D, Volcanoes in Victoria, Royal Society of Victoria, 1994
Ferrett, Russell, Australia's Volcanoes, Reed New Holland, 2005
Grimes, Ken, Volcanic Caves and Related Features, Field Guide: Limestone Coast 2004
Grimes, Ken, Tunnel Cave Mount Eccles, 2000
Department of the Environment, Water, Heritage and the Arts, Budj Bim National Heritage Landscape more information, http://www.environment.gov.au/heritage/places/national/budj-bim/information.html 26/10/2009
Parks Victoria, Mount Eccles National Park, http://www.parkweb.vic.gov.au/1park_display.cfm?park=153 26/10/2009
Wikipedia, Gunditjmara, Eumerella Wars, http://en.wikipedia.org/wiki/Gunditjmara#Eumerella_Wars 26/10/2009
Wikipedia, Lava, Volcanic morphologies, http://en.wikipedia.org/wiki/P%C4%81hoehoe#P.C4.81hoehoe 26/10/2009

Additional Hints (Decrypt)

Gur ynin orapu vf arne gur obggbz bs gur fgnvef

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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