The risk of volcanic eruption in mainland Australia
E B Joyce
School of Earth Science, University of Melbourne
Melbourne VIC 3010
ebj@unimelb.edu.au
SUMMARY
The young volcanoes of the Australian mainland are
made up of the Newer Volcanic Province of Victoria and
southeast South Australia (NVP), and a number of
separate provinces in far north Queensland. These
volcanic fields are similar in age, and in their numerous
scattered scoria and lava cones, extensive basalt flows,
and maar/tuff ring eruptions of phreatic origin. Australian
volcanologists and seismologists now agree that youthful
ages imply the possibility of further activity. A risk and
hazard map for the NVP (Joyce 2005) demonstrates that
volcanic activity must be considered a serious
environmental hazard and risk for the Australian
mainland.
Key words: volcanic, risk, hazard, Australia
INTRODUCTION
In southeastern Australia, nearly 400 small, monogenetic
scoria cones, maars and lava shields have been built up by
Strombolian/Hawaiian areal eruptions over the past 6-7 Ma in
the Newer Volcanic Province (NVP) of southeastern Australia
(Nicholls & Joyce 1989). Fluid basalt flows have spread
laterally around vents, often extending for many tens of
kilometres down river valleys. Where the lava flows have
blocked drainage, lakes and swamps have formed. Phreatic
eruptions have deposited ash and left deep craters, often now
with lakes. The youngest activity has been dated at 4000-4300
B.P.
In northeastern Australia, from Townsville and north to
Cooktown, eight distinct regions have been studied, and found
to show many of the features of southeastern Australia (Fig.
1).
VOLCANIC RISK AND HAZARD IN MAINLAND
AUSTRALIA
Most comments on volcanic risk and hazard on mainland
Australia refer to the southeastern Australia area and the
Newer Volcanic Province. However the conclusions reached
here apply equally to the extensive volcanic provinces of
similar type and age in northeastern Queensland, although this
area will not be discussed in detail.
Most suggestions regarding volcanic risk have been based on
the young appearance of volcanoes and their lava flows and
ash deposits. The explorer Major Mitchell recorded the
volcanoes of Southeastern Australia in 1836, just 170 years
AESC2006, Melbourne, Australia.
ago, and with the publication of his report in 1838 the
youthful appearance of the volcanic region’s features became
widely known. Accounts by Bonwick (1858) and BroughSmyth (1858) added to Mitchell’s observations, and the area
became well-known for its youthful volcanic features. With
the advent of radiocarbon dating the young age of many of the
area’s features was confirmed. Australian volcanologists and
seismologists now agree that the youthful age and probable
frequency of eruptions imply the possibility of further activity
in both southeastern and northeastern Australia, e.g. Blong
(1989) states that the "volcanism is so youthful that the
possibility of future intraplate eruption in the region cannot be
ruled out".
A second approach has been to develop an overall view of the
activity of the NVP (Hilmansyah 1985). Using K/Ar dates
which show the province began its activity some 5 Ma ago,
and a catalogue of eruption points which list approximately
400 volcanoes, simple arithmetic can be used to show the an
average separation between eruptions of 12 500 years. With
Mt Gambier the youngest dated volcano at some 4 000 to 4
300 BP, it can be argued that a further eruption is overdue.
A DETAILED CHRONOSEQUENCE APPROACH
A third approach is to attempt to describe in detail the
frequency of volcanic eruption over time. With fifty K/Ar
dates and a similar number of radiocarbon dates, there are
many gaps in the record, not the least being the problem of
relating dated flow samples to their points of eruption.
Recently attempts have been made to fill the gaps in the dating
record by using geomorphology and soils to group flows and
eruption points of similar age, and then use available dates to
assign ages to otherwise undated activity. This method is
discussed in more detail in Joyce (2005). Mapping of flows as
Regolith Terrain Units or Regolith Landform Units (Joyce
1999) have been assisted by the use of radiometric imagery
obtained by the Geological Survey of Victoria. A map of
flows by ages can then be used to give a list of volcanoes by
ages. Further work is needed, and in particular further dating
of the younger flows, ash deposits and volcanoes, but a pattern
of eruption over time is emerging, in particular a greater
frequency of activity during the last 30 000 to 50 000 years.
This suggests a frequency in recent times of some 2 000 years
between eruptions (Joyce 2005). A formal statistical study is
now underway.
This strikingly small period might be argued as too small, if
volcanoes were not evenly spread though time, but erupted in
groups or clusters, allowing for longer gaps between activity,
as suggested recently for the Auckland area of New Zealand, a
province with similarities to the NVP and north Queensland
provinces.
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Volcanic risk
E B Joyce
STUDYING SMALL MONOGENETIC
VOLCANOES
community, and for planners within local government and
emergency organisations.
Many provinces or fields with small monogenetic volcanoes
are found across the globe, and many are of post-Miocene age,
and were catalogued in a study by the IAVCEI, and the
southeastern and northeastern Australia data was compiled but
unfortunately not published. However the catalogue from
southeastern Australia has provided much detail for further
analysis.
Where are the volcanologists with experience in such areal,
monogenetic eruptions? Australian volcanologists have
worked on major volcanoes in active areas such as Papua New
Guinea and the Pacific islands. Much expertise with large
active volcanoes also exists in New Zealand. Perhaps the best
assistance would come from volcanologists who are familiar
with the past four decades of activity on the big island of
Hawaii, where a scoria cone and a lava shield have been
constructed, and numerous flows have destroyed infrastructure
and led to the evacuation of local residents, as well as the need
to look after the many tourists who have been attracted to such
relatively benign eruptions.
Such volcanoes are found in France and Germany, in the
southwest United States, in East Africa, Central and South
America, and across the Pacific including in New Zealand.
Most are young, and often strikingly so, but few have been
active in historical times. Maar eruptions have been observed
in Alaska, and the eruption of Paricutin in 1943 in Mexico, in
a closely-settled farming area, was well-recorded by the
United States Geological Survey, from the early and rapid
cone construction, then the formation of a lava field and ash
deposits which damaged or destroyed villages and farm land,
to the current fumarolic stages sixty years later.
Other models for future eruption can be based on observation
of the small scale activity of cone building and lava flows
observable on such large volcanoes as Mt Etna, but the best
studied analogue is the continuing and now 40 years old
eruptions in the east rift zone of Kilauea, on the big island of
Hawaii, recorded in great detail by the USGS, and studied by
many local and visiting volcanologists.
CONCLUSIONS
A scenario for southeastern or northeastern Australia can be
presented in which several volcanoes, perhaps of different
types (maar, eruption scoria cone building, extensive lava
flows production) might occur at intervals of say 5,000 or
10,000 years. Such scenarios focus our attention on what sort
of complex volcanic activity emergency response
organisations and the community should be preparing for.
Little warning of an eruption would be expected. Minor
seismic activity with small earthquakes might precede the
eruption by some weeks, and there could also be minor uplift
or subsidence of the ground surface, and perhaps changes in
ground temperature, and the exhalation of volcanic gases and
steam.
Maar activity upwind of a town or one of the major cities of
the region, such as Melbourne or Ballarat, would provide
particular problems from ashfall and base surge flows. In
contrast, lava flows would follow the general slope and mostly
move southwards down pre-existing valleys (Fig. 2). Hazard
impacts of lava and ash would include property and
infrastructure damage; effects on people, farm animals and
crops; water pollution and stream derangement; and grass and
forest fires. There could be associated earthquakes and ground
deformation. Emergency management would be concerned
with evacuation planning, diversion or control of flows,
removal of ash and scoria from roofs and roads, control of
fires and floods, and the repair and rebuilding of
infrastructure, especially roads and bridges. Government
bodies should be planning for preparedness and mitigation,
and eruption scenarios should be developed and publicised.
Public education will be necessary, both within the local
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Figure 1. Young volcanic areas of Australia. A: Maer,
Torres Strait; B & C: Sturgeon, Nulla, Chudleigh,
McBride, Wallaroo, Atherton, Piebald & McLean; D:
Bundaberg & Gayndah; E: Eastern Uplands; F: Western
Victoria; G: southeastern South Australia.
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E B Joyce
REFERENCES
Blong, R.J. 1989. Volcanic Hazards, in Johnson, R.W. (ed.):
Intraplate volcanism in eastern Australia and New Zealand. Cambridge University Press: 85-88.
Bonwick, J. 1858. Western Victoria, its geography, geology
and social condition. Thomas Brown, Geelong (reprinted
Heinemann Australia, 1970).
Brough-Smyth, R. 1858. On the Extinct Volcanos of Victoria,
Australia. Quarterly Journal of the Geological Society of
London, 14, pp. 227-235.
Hilmansyah, L. 1985: A volcanic hazard assessment of the
Newer Volcanics in Victoria and New South Wales. unpublished M.Sc.thesis, University of NSW.
Johnson, R.W. (ed) 1989. Intraplate Volcanism in Eastern
Australia and New Zealand. Cambridge University Press,
Cambridge.
Joyce, E. B. 1999. A new regolith landform map of the
Western Victorian volcanic plains, Victoria, Australia, In
Taylor, G & Pain, C. (eds) Regolith ‘98, Australian Regolith
& Mineral Exploration, New Approaches to an Old Continent,
Proceedings, 3rd Australian Regolith Conference, Kalgoorlie,
2-9 May 1998, CRC LEME, Perth, pp.117-126.
Joyce, Bernard, 2005. How can eruption risk be assessed in
young monogenetic areal basalt fields? An example from
southeastern Australia.
Special issue on volcanic
geomorphology, Zeitschrift fur Geomorphologie NF, Suppl.Vol. 140, 195-207.
Mitchell, T.L., 1838. Three expeditions into the interior of
Eastern Australia. T. & W. Boone, London, 2 vols.
Nicholls, I.A. and Joyce, E.B., 1989. Newer Volcanics,
Victoria and South Australia, East Australian Volcanic
Geology, in R.W. Johnson (ed), Intraplate Volcanism in
Eastern Australia and New Zealand. Cambridge University
Press, Cambridge, pp. 137-143.
Figure 2. Mapping of eruption types and ages with an indication of volcanic risk and hazard for the Newer Volcanic Province
of southeastern Australia (Joyce 2005).
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