Transcript TAMBORINE MOUNTAIN - Tamborine Mountain Landcare Inc

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