Have you ever wondered how water can spring up from the ground near the top of a mountain?
Barney Creek, which emerges from the ground near the top of the East peak of Mount Barney, is a good example of this phenomena. It runs consistently, even during very dry conditions. Where does the water come from?
Firstly, a quick explanation of how Mount Barney was formed. You can learn more from “Mount Barney EarthCache” GC2G23Z.
Mount Barney is the product of a large volcano that erupted about 24 million years ago. The volcano emerged as the Australian crust moved slowly northwards over a ‘hot-spot’ in the Earth’s mantle below. Initially there was an up-doming and tilting of the previous sandstones and shale rocks of the district. Then, the first eruptions happened which were of basalt lava. Later, the magma below changed to rhyolite, and a large mass accumulated at depth. Some of this mass began to cool to larger crystals. Then, suddenly, a huge surge of pressure thrust this mass upwards 2400m to near the surface, adjacent to the volcano’s central vent. It cooled to a rock called granophyre, coarser grained than rhyolite.
The pressure also dragged up some very old rocks, namely marine sedimentary rocks, laid down on the continental shelf about 320 million years ago. Since those times, erosion has stripped away the softer sedimentary rocks, leaving the hard granophyre and rhyolite as Mount Barney as we see it today.
Back to where the water comes from; moisture which evaporates from the ocean is carried by the prevailing onshore winds towards the drier and hotter inland areas. When these winds encounter mountain ranges, such as Mt Barney and the surrounding Great Dividing Ranges, the moist air is driven upslope towards the peak, where it condenses into clouds and falls as rain on its upper slopes, known as the “recharge area”. Mountain peaks, such as Mount Barney therefore receive significantly higher rainfall than lowland areas.
Generally, the higher the mountain, the thinner the soil. So, unlike lowland areas, not much water can be absorbed by the soil. Instead, it seeps through cracks in the rock where, over time, weathering will cause the rock to dissolve making it more pervious. Bigger fissures are created where the water then accumulates. The water "flows" down within the mountain. If a layer of deeper impervious rock, such as granophyre or rhyolite, lies under the more porous rock above, the water cannot move downwards any further and will move horizontally and emerge from the side of the mountain as a spring.
The water then flows downhill as a creek, growing as other spring flows join it. Barney Creek emerges below the East Peak of Mount Barney and flows down just below Rum Jungle bush campground in the saddle between the East and West peaks.
To claim this Earthcache you will need follow the creek upstream from Rum Jungle Campground to the published coordinates. Then answer the following questions:
Q1: Do you think this location is the source of Mt Barney Creek or is it higher up. Give reasons for your answer.
Q2: Is there a single exit point for the “spring” or are there others nearby?
Q3: Are the rocks in this area different in colour and texture than those of the surrounding slopes. If so, why do you think this is?
Optional: Take a photo of your party at Barney Source.
To access GZ for this Earthcache you’ll need to climb Mount Barney, which is a difficult and strenuous bush walk.
More info here: https://parks.des.qld.gov.au/parks/mount-barney
Navigation: There are no formed tracks from Rum Jungle. You have 3 choices depending on your preference of terrain and prevailing conditions.
- Head up along the ridgeline directly from Rum Jungle. There are several rocky outcrops you’ll need to negotiate; some scrambling is required and there are some steep drop-offs (recommended route).
- Drop down from Rum Jungle until you reach Barney Creek. Rock hop upstream until you reach GZ. There are some sections where you’ll need to leave the creek to avoid large boulders and vegetation.
- Continue over the creek, past the Old Hut site and follow the obvious foot pad towards the East Peak until you gain enough altitude to contour across to GZ. The terrain and vegetation is generally more open here after recent fires, but this may change with time.
N.B. You can log this Earthcache immediately after sending in your answers, without waiting for the owner's approval. However should your answers be incomplete or inappropriate, your log may be deleted.
References:
https://parks.des.qld.gov.au/
https://www.quora.com/
https://en.wikipedia.org/