A volcano filled with water. Erupted 4500 years ago
The Western Victorian Volcanic Plains are the third largest in the world and exceeded only by the Deccan in western India, and the Snake River Plateau in the United States ( Idaho-Nebraska ).
The Victorian Volcanic Plains are located in Western
Victoria and covers over 2.3
million ha (10.36% of the State).
It
stretches from Portland in the west
to Craigieburn in the east and from
Clunes in the north to Colac in the
south.
Climate and geology.
The Victorian Volcanic Plain bioregion is characterised by vast open areas of fertile
plain covered with grasslands and grassy woodlands, and small patches of open
woodland.
The bioregion is interspersed with stony rises and numerous extinct
volcanic eruption points, denoting old lava flows and numerous scattered large
shallow lakes and wetlands.
Few major rivers cross the plain, the most significant of
these include the Barwon, Hopkins, Leigh, Maribyrnong, Wannon and Werribee
Rivers and Mount Emu Creek and their tributaries.
The basalt plain was formed by extensive volcanic activity mostly from the Upper
Cainozoic era (Quaternary) from approximately 6 million years ago to as recently as
7,200 years ago at Mt. Napier.
Several types of lava flows occurred including sheet
flows and constricted flows along valleys.
Irregular and chaotic stony rises occupy
large areas of the plains.
Numerous volcanic cones dot the landscape with scoria
cones being the most common (e.g. Mt Elephant, Mt Napier and Mt Noorat)
although some basalt cones are present (e.g. Mt Cottrell).
Soils are generally
shallow reddish-brown to black loams and clays (Conn 1993). They are fertile and
high in available phosphorous.
Older flows in the Cressy and Hamilton areas have
allowed a greater development of deep soils.
Dark saline soils occur around the
margins of some lakes.
Amongst the basalt are geological remnants that precede
and survive the period of vulcanism that produced the “Plain”.
The majority of the
elevation is below 250 m above sea level, however the maximum height does reach
720 m above sea level at two locations, Mount Doran and Mount Egerton, east of
Ballarat.
Most of the region receives between 500 and 700 mm of rain per annum (Conn
1993) with rainfall distributed relatively evenly throughout the year except in the
higher rainfall areas of the south west which receive a higher proportion of rainfall in
winter.
The general pattern of climate is one of gradation rather than fluctuation.
Average yearly rainfall generally decreases from southwest to northeast across the
region.
Annual average rainfall figures are 840 mm for Portland, 720 for Colac, 680
for Hamilton, 630 at Skipton, 530 at Cressy and 450 at Eynesbury.
The warmest
months are January and February with mean maximum temperatures ranging from
about 20° to 27°C.
In winter the mean maximum is as low as 10°C with a mean
minimum of 3°C.
The Western Victorian and Eastern South Australia Volcano Map
Each dot represents where volcanic activity had occurred.
Current active volcanoes in Australian territory are located on Heard and McDonald Islands in the Southern Ocean, about 4100 kms southwest of Western Australia.
Is there a risk of a volcanic eruption ?
Volcanoes in eastern Australia that have not
erupted in thousands of years still pose a threat and emergency
services should be better prepared, an expert told a geology
conference today.
But another expert thinks Australia should
be more worried about fires, storms and earthquakes than
volcanoes.
Bernie Joyce, from the
University of
Melbourne, presented a paper on volcanic hazards today at the
17th Australian
Geological Convention of the
Geological Society of Australia held in Hobart,
Tasmania.
View Recent Volcano Observatory Activity Reports Volcanoes in Victoria, New South Wales and
Queensland could erupt at any time, he told ABC Science
Online ahead of the conference.
There has been no
volcanic activity in Australia in the past few hundred years, and no
major eruption since Mt Gambier, on the border of South Australia
and Victoria, 4500 years ago.
But a sudden eruption could
still catch emergency authorities unprepared for the floods, mud
flows and ash falls that could follow, said Joyce.
He said
the kind of eruption Australia could expect was not on the same
scale of the Mt Helen's eruption, which wiped out a large area in
the U.S. state of Washington in May 1980. Australia could expect a
smaller eruption.
"We haven't had much [volcanic] activity in
the last few hundred years, so we're not quite sure what it would
look like," said Joyce.
According to Joyce, an eruption could
either be an explosion like the one at Mt Gambier, creating a big
hole in the ground, or avolcanic eruption common in Queensland and
Victoria in the past 50,000 years of a different type.
These
eruptions have large lava flows followed by a more gaseous eruption
where the lava breaks up into small pieces and builds a cone of
cinders and sharp rock material.
There is evidence of these
cones and crater lakes around Victoria and northern Queensland,
Joyce said.
"In either case you wouldn't get much warning and
you would be working out what to do when it came," Joyce
said.
Eastern Australia had up to 20 volcanoes less than
50,000 years old, said Joyce, who said probability showed these
still posed a threat.
Joyce warned the consequences of even a
small eruption coming into contact with groundwater could include
hot, wet ash falls, dangerous gases and ash blown into the air,
damage to animals and the environment, and pollution in water
systems.
Reference http://www.17thagc.gsa.org.au/
The usual warning signs.
But Dr Wally Johnson,
head of the geohazards division at Geoscience Australia told ABC Science
Online that Australia's government geological science
organisation was more concerned about hazards posed by fires, storms
and earthquakes than volcanoes.
"Australians are more likely
to face risks from volcanoes when flying to Southeast Asia or the
South Pacific and ash from volcanoes getting into the jets and
causing problems with aircraft," said Johnson.
While Johnson
said that Joyce did a good job raising awareness of the risks posed
by volcanoes, he said there were other hazards with higher
priorities.
"If Mt Gambier did erupt it would impact on local
communities," Johnson said. "But any changes to the state of these
volcanoes would be noticed early on, either through earthquakes, or
in the case of Mt Gambier an increase in the temperature of the
water.
"We know that volcanoes do provide a fair bit of
warning. In most cases this would be months or even years. You might
get a volcano way out in western Victoria where you might not notice
the warning signs but in most cases you'll get advance warning from
geological phenomena," he said.
Advance warnings could
include an increase in seismic activity, a change in the temperature
of surface soils, or even smoking fumaroles, small eruptions from
the side of a volcano that indicate that a major eruption was
imminent.
The big earthquake still building SE Australia
Two separate geological studies have concluded that an area from
Adelaide to south-east Victoria is seismically active and the next
'big
one' could endanger lives and infrastructure.
Contrary to the popular notion that Australia is an ancient continent
that has for millions of years been geologically comatose, University of
Melbourne geologists have uncovered evidence that parts of South-eastern
Australia recently stirred from their geological slumber and are in an
active mountain building phase. These mountains are being shaped by
earthquakes, some reaching greater than 6 on the Richter
scale.
"When these big quakes reoccur, they have the potential to
cause catastrophic damage to cities such as Melbourne, Adelaide, and the
La Trobe Valley area, which straddle some of these major faults lines,"
says Professor Mike Sandiford, who conducted one of the studies.
Possibly, the most dramatic indication of this geological
stirring, which the studies estimate began suddenly about ten million
years ago, can be found in the landscape of the Mount Lofty Ranges near
Adelaide.
"Some faults around Adelaide have moved slabs of the
continent up to 30 metres in the last one million years," says Sandiford.
"A typical earthquake of magnitude 6.0 might produce a
displacement of about one metre. Thirty metres is equivalent to 30-50 big
earthquakes in the last million years," he says.
Other areas of
intense mountain building have been around Victoria's Otway Ranges,
Mornington Peninsula and Strzeleckis. In some of these areas, similar
uplift and erosion over the last 10 million years have thrust chunks of
Australia upwards in the order of one kilometre.
Tectonic
movements have pushed the Otways 250 metres higher in the last three
million years, and The Selwyn fault, which runs from Mt Martha, on
Victoria's Mornington Peninsula, east to the Dandenong Ranges has possibly
produced six metres of uplift in the last 100,000 years.
"This is
potentially six big earthquakes," says Sandiford.
"We are still
trying to determine the slip rates along these fault lines, but our
evidence so far suggests that we should expect, on any one of the major
faults, a large earthquake every 10-20,000 years. The estimated return
period of a quake greater than 6.0 in south-east Australia is about 30
years, but none have been recorded in the last 100 years," he says.
"Most earthquakes experienced by this region are less than three
on the Richter scale and occur several times a year. It is unusually quiet
at the moment with nothing over 1.5 for the last few months."
Sandiford's evidence for the mountain building comes from
extensive airborne geophysical data that measure radioactivity and
magnetic field of the soil and rock. Rocks of different ages and types
display different levels of radioactivity and magnetic properties. Faults
and uplift which bring older rocks to the surface or bury younger strata
can be detected through such measurement.
A second study led by
the University's Dr Malcolm Wallace investigated sediments and seismic
data from petroleum surveys to determine the long-term history of
earthquakes and seismic activity in South East Australia.
Evidence
of faulting, buckling and uplift can be clearly seen in the young sediment
record from this region. The team obtained an age for the various faults
and folds by using a combination of fossils and radioactive isotope dating
methods.
The findings confirm that the young mountain building and
earthquake activity began around 10 million years ago and continues to the
present day.
"This young faulting and folding has had very
important economic effects for Australia. The giant oil and gas fields of
the Gippsland Basin are largely trapped in young geological deformations
produced by the seismic activity. Faulting, however, can also rupture the
reservoirs and cause leakage.
"In the La Trobe Valley it is this
tectonic activity that has made the thick sequences of brown coal that
Victoria relies on for its power generation economically accessible," says
Wallace.
In the Murray Basin, the same activity was largely
responsible for the heavy mineral deposits such as titanium and rare
earths. It also caused the damming of the Murray River only 60,000 years
ago forming the Barmah Swamp near Echuca, Victoria.
"While this is
still nothing compared to the activity along the plate margins of, for
example, New Zealand and California, it defies the notion that Australia
is an inactive continent," says
Dr Wallace's research team is
Julie Dickinson (PhD student) and Dr Guy Holdgate, all from the
University's Department of Earth Sciences.
View Recent Earthquake Monitor with location map
View Daily Earthquake activity Reports latest news feed
View All Alerts and News Feeds
The first reported earthquake in Australia was felt at Port Jackson (Sydney) in June 1788, when Governor Phillip reported:
"The 22nd of this month we had a slight shock of an earthquake; it did not last more than 2 or 3 seconds. I felt the ground shake under me and heard a noise that came from the southward, which I at first took for the report of guns fired at a great distance."
Similar earthquakes were felt in the early days of Adelaide (1837), Melbourne (1841), Hobart (1827) and Perth (1849).
The map shows earthquakes with Richter magnitudes greater than 3.5 and suggests the higher seismicity and hazard regions are along eastern Australia (in bands running from Melbourne to Newcastle, Brisbane to Gladstone, and Mackay to Cairns), in the Adelaide geosyncline, and in parts of Western Australia. Less seismographs and lower population density during the last century in Queensland relative to eastern NSW and Victoria means that the true seismicity in Queensland compared to eastern NSW and Victoria may be higher than it appears on the map
Map of Victoria click here to enlarge.
Volcanism over the last 60 million years has occurred down the east coast of Australia.
Volcanologists have
divided this volcanic activity into lava fields - areas where large
amounts of lava flowed from diffuse dykes and pipes over a wide area
(shown in red); and central volcanoes - areas where volcanism was
produced from either a single central vent or a cluster of vents
(shown in orange).
It is now thought that the central volcanoes were
produced as the Australian continent moved over a hot spot in the
underlying mantle which 'melted' through the plate to form the
volcano. As the continent moved northward, the stationary hot spot
formed volcanoes further to the south on the continent. Therefore
the rocks of central volcanoes down the east coast become younger as
you move southward.
Map courtesy. http://www.ga.gov.au/archive/volcanoes/
Hotspot system in our backyard
We have a hotspot system of our very own. Australia's hotspot currently lies under Victoria, Bass Strait, Tasmania, and the floor of the Tasman Sea at a latitude of about 40°S. It's one of more than a hundred systems identified around the world.
As far as hotspots go, the one in our backyard is slumbering. Present hotspot activity is possibly confined to the triggering of earthquakes in predicted areas, such as the recent event off the coast of north-west Tasmania, and deep gas discharges under Victoria and Tasmania.
Scientists believe a new Australian volcano is being created.
Geologists suspect an earthquake that originated 50 kilometres from King Island in February 2002 signalled the reawakening of the hot spot, a region in the Earth's crust where the planet expels some of its internal heat.
Australia's hot spot is several hundred kilometres wide and lies under Bass Strait and parts of Victoria and Tasmania.
Wally Johnson, a vulcanologist at Geosciences Australia, said the fact that there were earthquakes taking place in the area "means that geologically, the hot spot has to be regarded as active, even though it hasn't produced volcanic eruptions as such".
He said it could spawn a volcano within 100 years
One chain of about 13 volcanoes begins in north Queensland.
2008, 2007, 2006, 2003-04, 2000-01, 1993, 1992, 1985-87, 1954, 1953,
1950-52, 1910, 1881? McDonald Island began erupting in 1992, after lying dormant for 75,000 years. It has erupted several times since with satellite pictures in 2001 showing that the island had doubled in size. The initial evidence came in the form of abundant pumice washing up on beaches north and south of The Spit at the eastern extremity of Heard Island, directly to the east of McDonald island.
This is Australia's second currently active volcano.
Reference: ABC Science Online
The largest in this chain is the Tweed Volcano, where Mount Warning represents the main vent. The chain extends south from the Cape Hillsborough Volcano in north Queensland through to the Mount Macedon Volcano in Victoria.
Other volcanoes in the chain include the Glasshouse Mountains, the Warrumbungles and Canobolas near Orange. The volcanoes are quite young. The oldest ones are found in north Queensland, while the youngest are in Victoria - the most northern volcano formed around 33 million years ago.
Another chain of hotspot volcanoes extends along the floor of the Tasman Sea and includes the Gascoyne seamount.
Active Australian Volcanoes.
Heard Island and McDonald Islands is a subantarctic island group located in the Southern Ocean, about 4100 kms southwest of Western Australia.
The islands and surrounding waters teem with wildlife and other natural wonders that make it a special place.
Heard Island consists of 2 volcanic cones, Big Ben and Mt. Dixon, joined by a narrow isthmus. Both cones are young, but only Big Ben has been observed to erupt.
Big Ben is a large, glacier-covered, composite cone 20-25 km in diameter at sea-level, consisting mainly of basaltic lavas and lesser ash and scoria. Its summit region consists of a SW-facing semi-circular ridge 5-6 km in diameter, 2200-2400 m above sea-level.
Night-time view of Big Ben erupting on 3 February 2001, viewed from Atlas Cove.
Stu Fitch
Courtesy Australian Antarctic Division © Commonwealth of Australia
2006
Heard Island Volcano Eruptions 53.106 S, 73.513
E
View of the outline of the caldera of Camels Hump - Mount Macedon.
Lethal Australian Ants.
Reference: Geoscience Australia http://www.ga.gov.au/
Reference: Australian Antarctic Division http://www-new.aad.gov.au/default.asp?casid=2099
Reference: Australian Antarctic Division http://www-new.aad.gov.au/default.asp
Reference: Global Volcanism Network's
http://users.bendnet.com/bjensen/volcano/indian/indian-heard.html
Reference: Volcanoes & Earthquakes in SE Australia http://www.seismicity.segs.uwa.edu.au/welcome
Photograph of South Australian Volcano
Courtesy. Office of Minerals & Enenrgy Resources, South Australia.
Images from poster by B. Joyce (University of Melbourne), Cities on Volcanoes Conference, Aukland, N.Z. Feb 2001
Map courtesy. http://www.ga.gov.au/archive/volcanoes/
