TAMBORINE MOUNTAIN Geology & Groundwater Origins
Mar 26, 2015
TAMBORINE MOUNTAIN
Geology
&
Groundwater Origins
Tamborine Plateau
• Formed on horizontal basalt lavas
• Erupted from the Tweed Volcano over Mt Warning in NSW ~23 million years ago
• One of several volcanoes active at that time
Erosion
• Plateau is remnant of the final surface of the northern flank of volcano
• Isolated by erosion from the radial streams of Canungra Creek and Coomera River
• Same surface still visible to south on Beechmont
The basalts cap four groups of older rocks-
• Meta-sediments’ of Neranleigh-Fernvale beds on east
• Rhyolite lavas of Chillingham Volcanics in centre
• Thin band of soft shales of Ipswich Coal Measures
• Sandstones of Woogaroo Subgroup on west
The basalts
• Lowermost flows are of the Albert Basalt from Focal Peak Volcano –limited in extent
• Remainder are of the Beechmont Basalt from Tweed Volcano
• Several sub-units recognised
Beechmont Basalt
• Unit A – 10 thin flows with inter-bedded sediments• Unit B, Cameron Falls Member – Single massive
flow 20m thick• Unit C – 4 or 5 thin flows• Unit D, Eagle Heights Member – Single massive
flow 25m thick forming upper scarp of mountain• Unit E – Weathered flows on plateau surface
• (Lower units absent on eastern side)
Beechmont Basalt (contd.)
• Thin flows of Units A and C are strongly fractured and contain zones of gas bubbles
• These less resistant to weathering and form benches on sides of mountain
Water movement
• Rainfall seeps into ground to saturate rock
• Level of saturation is the water table
• Just because rock is saturated does not mean water can be extracted – often held only in tiny pores and fractures
• Water can only be pumped where there are permeable zones which allow it to flow and be replenished relatively quickly
Controls on groundwater at Tamborine Mountain
• Horizontal basalt flows• Fractures and gas bubbles in Units A & C
which create permeable layers that feed groundwater laterally on to the sides of the mountain to form springs
• Springs wax and wane depending on pressure head of water table, which is seasonally variable
• Other permeable layers at base of basalt
Likely water sources
• Best flows are likely from bores in Units A & C, and in deeper permeable layers at base of basalt sequence
• Units B and D unfavourable, but small flows may be possible from localised fracture zones
• Older rocks beneath basalt not of significance