3.0 The Environmental Context
3.1 Introduction
The following section describes the environmental context of the Lake Burley Griffin Study Area,
particularly focusing on the ‘pre-lake’ environment. The discussion of the evolution of the landscape
through geological time describes how the key landscape features developed into their present forms.
The vegetation which covered the pre-settlement landscape is also described. This description of the
environmental setting of Lake Burley Griffin and its foreshores will allow comparisons (in later sections)
between its present form and its earlier natural state, and provide a picture of how the current landscape,
environment and natural values evolved.
3.2 Geology and Geomorphology
3.2.1 Earliest Sedimentary Deposition
The dominant geology of Lake Burley Griffin and its immediate catchment is of the Ordovician and
Silurian Periods (480–416 million years before present). The oldest rocks are the Ordovician
sedimentaries (sandstones, mudstones and shales) now exposed only in a band crossing the lake area
diagonally between the Deakin and Acton Faults. The Early Silurian sedimentary deposits, belonging to
the Black Mountain Sandstone and State Circle Shale formations, also occur along this band. The
extent of these formations and those described below is shown at Figure 3.1.
The earliest Ordovician formations, by their fossil record, were laid down when the Canberra region (and
most of southeastern Australia) was under deep sea water. The uplifting, folding and subsequent
extreme weathering of these formations indicates that, for a time, the rocks were elevated above sea
level. This eroded surface was again covered by the sea during the Early Silurian Period because the
Black Mountain Sandstone and State Circle Shale formations show fossil evidence of a deep water
environment, away from land.1
3.2.2 Limestone Plains
The next depositional phase appears to follow another period of uplift and dry land weathering because
the Middle Silurian Canberra Formation (mudstone, sandstone and limestone) was laid over a shallow,
submerged hilly landscape. This now underlies the centre and eastern part of the lake and environs,
and is presently exposed in the Parliamentary Triangle, Civic, Manuka, Narrabundah and Fyshwick
areas. It was from examples in these exposures that the name ‘Limestone Plains’ derived.
3.2.3 Volcanic Phase
Interspersed with the sedimentary layers of the Canberra Formation are tuffs and ashes, indicating the
beginning of a period of volcanic activity in the region which was enough to raise the land above sea
level once again.2
Extensive volcanic activity in the Middle and Late Silurian Periods formed the Ainslie Volcanics, Mount
Painter Volcanics and the Deakin Volcanics. The youngest of the marine Silurian rocks, the Yarralumla
Formation shales which make up Red Hill, are sandwiched by large areas of volcanic rock. The Mount
Painter Volcanics are the most extensive, occupying the area west of the Deakin Fault.
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
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3.2.4 The First Molonglo Lake Landscape
There are no rocks in the Canberra region from the end of the Silurian to the late Tertiary Period. During
this time, major uplift and movement events occurred in southeastern Australia and formed the main
geomorphology of the Canberra region. This is the horst-graben-horst sequence across the region
corresponding to the Brindabella Range, Canberra area and Queanbeyan Hills respectively. The local
topographic features of Black Mountain, Mount Ainslie, Mugga Mugga and Red Hill are the more durable
rocks remaining after the weathering of the central graben area by the ancient Molonglo River and its
tributaries gradually lowered the softer surrounding landscape.3
The next significant geomorphological event occurred in the Pleistocene Epoch of the Quaternary Period
(around 2 million years ago). Öpik4 has pointed to evidence that scree falls from Black Mountain (which
consolidated into formations called ‘fanglomerates’ during a dry interval of the Pleistocene Ice Age)
dammed the Molonglo River and Sullivans Creek to form lakes along the courses of both waterways.
The approximated extent of the ancient Molonglo Lake was charted by Öpik (see Figure 3.2) and closely
mirrors the present Lake Burley Griffin. He postulated that after the rivers had finally broken through the
obstacles, the lakes disappeared, leaving behind the sandy river flats. Subsequent work by Brown and
Ollier5 supported the existence of the Sullivans Creek lake but could not confirm Öpik’s delineation of a
Molongolo River lake, suggesting instead a series of changing channels and terraces over a similar
area. More recently, Henderson and Strusz list the unconsolidated sands, clays and gravels of the old
lake beds and the remnant sand dunes at Russell and Pialligo as evidence of ancient lake-forming
processes.6
3.3 The Biophysical Environment
The pre-European vegetation of the area comprised eucalypt dry open forest on the hills and upper
slopes, grassy woodlands on the lower slopes and river flats, and riparian forest (Casuarina and
eucalypt) along the waterways.
The open forest areas of the uplands were unsuitable for farming and consequently many of these forest
areas remain, providing indicators of previous vegetation cover. However, much of the existing
vegetation can best be described as ‘modified natural’ and represents remnants of the pre-European
vegetation, in a changed structural and floristic form. Other remnants are more modified, having some
native species present but are substantially altered through reduced density or removal of some layers
of vegetation.7
The four prominences surrounding Lake Burley Griffin, which provide its immediate ‘bushland setting’,
are each of a different geological and soil type. However, their forest cover is remarkably consistent.
Complete structural and floristic analyses of the vegetation communities separate them into distinct
ecological entities, but the same group of species occur as dominants in the open forest and woodland
communities of the area. This is an indication of the overriding effects of climate (especially the number
of frost free days) and elevation in determining the vegetation of the Canberra region, and the
correspondingly lesser effect of geology and soils.
3.3.1 Black Mountain, Acton Foothills and Stirling Park
Black Mountain comprises hard sandstones and has a vegetation community dominated by the red
stringybark (Eucalyptus macroryncha)–scribbly gum (Eucalyptus rossii) alliance. Within this alliance,
brittle gum (E. mannifera) and yellow box (E. melliodora) achieve local dominance in patches on the
upper slopes. At lower elevations (including the Acton foothills), scribbly gum is replaced by Blakeley’s
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Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
red gum (E. blakeleyi) and red box (E. polyanthemos). Throughout, the dominant understorey is tussock
grass (Poa spp.).8
The same vegetation alliance extends across the lake to Stirling Park, which is also on surface geology
of the Black Mountain sandstone formation. Not as high as Black Mountain, the ridgeline of Stirling Park
lacks red stringybark and instead is dominated by scribbly gum (Eucalyptus rossii) and brittle gum (E.
mannifera), with extensive stands of yellow box (E.. melliodora), Blakeley’s red gum (E. blakeleyi) and
apple box (E.. bridgesiana) occurring on the slopes.
3.3.2 Mount Painter and Stromlo Foothills
The surface geology of these areas is the Mount Painter Volcanics. Only on Mount Painter does native
forest vegetation survive; however, the same association would have covered the slopes to the south of
Mount Painter down to the Molonglo River, before they were cleared for agriculture. The dominant
vegetation is a Blakeley’s red gum (E. blakeleyi)–yellow box (E. melliodora) association, with isolated
apple box (E. bridgesiana) and brittle gum (E. mannifera).9
3.3.3 Red Hill
Red Hill is on the shales and calcareous shales of the Yarralumla Formation. It supports a woodland
association of yellow box (E. melliodora)–Blakeley’s red gum (E. blakeleyi), with scattered apple box (E.
bridgesiana) as a sub-dominant. Apple box (E. bridgesiana) and silver wattle (Acacia dealbata) are on
the eastern slopes. Other local dominants recorded include red box (E. polyanthemos)–scribbly gum
(Eucalyptus rossii), with broad leaved peppermint (E. dives), apple box (E. bridgesiana) and drooping
she-oak (Allocasuarina verticullata).10
3.3.4 Mount Ainslie and Russell Foothills
The Mount Ainslie volcanics consist of dacite lava (formed essentially of feldspar, quartz and biotite).
The formation supported dry sclerophyll forests of red stringybark (Eucalyptus macroryncha)–scribbly
gum (Eucalyptus rossii) on the higher ground, grading into yellow box (E. melliodora)–Blakeley’s red
gum (E. blakeleyi) woodland with scattered apple box (E. bridgesiana) on the lower slopes. The open
forest also includes brittle gum (E. mannifera), red box (E. polyanthemos), apple box (E. bridgesiana),
snow gum (E. pauciflora) and hill oak (Casuarina stricta).11
3.3.5 Limestone Plains
The plains below these high points were a patchwork of woodland, grassy woodland and grasslands.
The woodland and grassy woodland were not distinct floristic or even structural formations. They were
charcterised by the co-dominant canopy species of yellow box (E. melliodora) and Blakeley’s red gum
(E. blakeleyi), with apple box (E. bridgesiana) along ephemeral drainage lines. The density of canopy
trees varied from 10% to 30% coverage, with communities at the lower end of the density range classed
as grassy woodlands and communities at the upper end classed as woodlands. The areal balance
between the two would have varied as a result of fire regimes, with the woodland form being dominant at
some periods and the grassy woodland at others. The understorey of both was characterised by
tussock grasses of kangaroo grass (Themeda triandra) and spear grasses (Austrostipa spp).
The grasslands were part of the highly variable natural temperate grasslands of the Southern
Tablelands. This is an ecological community dominated by moderately tall or tall (up to 1m) dense to
open tussock grasses with a significant representation of forbs (other non-woody plants). It can be
treeless or have trees up to 10% cover. Enough of the ‘entirely treeless’ grassland mapped by Prior12
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
35
remain to give an indication of its floristics on the Limestone Plains. The dominant grasses were
kangaroo grass (Themeda triandra), spear grasses (Austrostipa spp) and wallaby grasses
(Austrodanthonia spp), with river tussock (Poa labillardieri) in the lower elevations. Common forbs were
sedge (Carex appressa), common everlasting (Chrysocephalum apiculatum), button wrinklewort
(Rutidosis leptorrhynchoides) and common sunray (Triptilodiscus pygmaeus).13
Riparian forest stands followed the courses of the Molonglo River and its perennial tributaries. This
existed mainly as ‘gallery’ stands of trees along the banks, but sometimes extended over sand banks on
the wider river meanders. In pre-European times, this forest would have comprised river oak (Casuarina
cunninghamia) and ribbon gum (Eucalyptus viminalis)14, with occasional patches of apple box (E.
bridgesiana).
3.3.6 Pre-European Vegetation Extent
A map of the pre European extent of these vegetation communities is provided at Figure 3.3. This map
has been derived from a number of sources of data. The grasslands distribution is derived from
estimates of the original extent of grasslands in the ACT Lowland Native Grassland Conservation
Strategy.15 This study was a refinement of the modelled distribution undertaken by Pryor in 193816,
adding survey data from all remnant sites, historical records and the mapping of cold air drainage.
The open forest, woodlands and riparian forest distributions have been derived from:

early photographs;17

the 1909 mapping by Scrivener;18

the 1929 aerial photographic survey of Canberra by the RAAF;19

species distribution notes in Pryor and Banks,20 Burbridge and Gray21, and NCDC22; and

field data collected from remnant vegetated areas for this heritage assessment.
The following structural communities have been delineated and mapped in Figure 3.3:
Structural
Community
Dominant Canopy Species
Open Forest
Eucalyptus macroryncha - E. rossii – E.. mannifera
E. rossii – E. dives – E. polyanthemos
E. melliodora – E. blakelyi +/- E. bridgesiana
Woodland
E. albens – E. melliodora – E. blakelyi +/- E. bridgesiana
Grasslands
Themeda – Austrostipa - Austrodanthonia
Riparian Forest
Casuarina cunninghamminana – E. viminalis – E.
bridgesiana
3.4 Biodiversity
It is difficult, and potentially misleading, to pinpoint the biodiversity values of the area before European
settlement, since species composition and richness would have varied with the dynamic transitions
between woodland, grassy woodland and grassland over time and with changing environmental
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Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
conditions (and Indigenous habitat modification). In addition to resident wildlife, the area is also
traversed by species migrating to and from the adjacent alpine areas.
3.4.1 Fauna Diversity
The Canberra Nature Park Plan of Management23 lists recordings of 12 different mammal species and
28 reptile and amphibian species for the combined open forest and woodland areas associated with
Black Mountain, Mount Ainslie, Mount Painter and Red Hill. A comparison with similar but relatively
undisturbed habitat areas (in Gould24) suggests that this is at or near natural levels for the area. The
same plan of management notes that the diversity of bird fauna in the ACT is due to not only the range
of natural habitats in the region, but also the habitats created by city gardens and parks, and the artificial
urban lakes. Of the 245 bird species recorded for the ACT by the National Parks Association25, only a
proportion would be indicative of the diversity present in the natural habitats of the Limestone Plains and
adjacent high ground. Invertebrates are the major component of animal biodiversity in grasslands, but
only the biodiversity ‘flagship’ species of the Golden Sun Moth (Synemon plana), Canberra raspy cricket
(Cooraboorama canberrae), Key’s matchstick (Keyacris scurra), and Perunga grasshopper (Perunga
ochracea) have been surveyed in any detail.
3.4.2 Flora Diversity
Black Mountain open forest and woodlands support around 500 plant species in 450ha. Aranda
bushland is also considered environmentally significant, with 220 native flora species. Comparisons in
Gould26 indicate that these species numbers are also at or near natural levels for the area. Red Hill, a
much more disturbed habitat, currently has approximately 105 different native plant species. Similarly, a
recent survey of Stirling Park27 recorded 101 native flora species.
Natural temperate grassland is very diverse. Recent surveys indicate that a total of more than 500
native and herbaceous species occur in these ecosystems in the Southern Tablelands.28 However, in
surveys undertaken in ACT lowland native grasslands since 1991, 50 species of grasses and over 200
species of native forbs (including sedges and rushes, lilies and orchids) have been identified.29 The
varying nature of species diversity in grassland is further illustrated by the recording of about 50
grassland species at Yarramundi Peninsula in 1996.30
3.5 Conclusions
This discussion of the environmental context of the Lake Burley Griffin Study Area shows that the
principle of designing with nature which was a central theme of Griffin’s work on Canberra is borne out
by the evidence of the landforms and landscape. The built features of Canberra and its central lake
were not imposed on the landscape, but have been fitted into it. The lake closely mirrors the shape and
extent of ancient lake or channel deposits on the same site. The forested hilltops and wooded slopes
bounding the lake are mostly intact visually and, on the basis of structure, floristics, and biodiversity, are
also largely intact biologically. Only the grasslands and riparian forest, which once covered the central
parts of the Limestone Plains, have been severely disrupted by later development. Surviving remnants
of these communities around Lake Burley Griffin will therefore have particular natural heritage value,
while the creation of the lake has in turn created a new ecosystem. The natural values of the lake as an
ecosystem are discussed in Section 8.0.
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
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38
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
Figure 3.1 Geology and geomorphology.
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
39
Figure 3.2 The hypothesised extent of an ancient Molonglo Lake.
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Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
Figure 3.3 Pre-European settlement vegetation (as discussed in Section 3.3.6).
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009
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3.6 Endnotes
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
42
Bureau of Mineral Resources 1981, The Geology of Canberra, Queanbeyan, and environs. 1:50,000 geological map and explanatory
notes, Australian Government Publishing Service, Canberra.
ibid.
ibid.
Öpik, AA 1958, The Geology of the Canberra City District, Bulletin No. 32, Department of National Development, Bureau of Mineral
Resources, Geology and Geophysics.
Brown MC and CD Ollier, 1975, Geology and scenery of Canberra, Australian Geographer, 13, p97–103.
Henderson, GAM and Strusz, DL 1982, Rocks and Fossils around Canberra, Bureau of Mineral Resources, Australian Government
Publishing Service, Canberra.
Environment ACT, 1999, Canberra Nature Park Management Plan 1999, Department of Urban Services Conservation Series No.14,
Australian Capital Territory Government.
ibid.
ibid.
ibid.
ibid.
Pryor, L 1938, The botany, forestry and zoology of the Australian Capital Territory on an ecological basis, in Handbook for Canberra, ed, K
Burns, ANZAAS Meeting, Canberra, January 1939, Canberra: Commonwealth Government Printer.
Environment ACT 2005, A Vision Splendid of the Grassy Plains Extended—ACT Lowland Native Grassland Conservation Strategy, Action
Plan No. 28, Arts, Heritage and Environment, Canberra.
Pryor, LD and Banks, JCG 2001 (2nd Edition), Trees and Shrubs in Canberra, Little Hills Press, Canberra.
Environment ACT, op cit.
Pryor, op cit.
NCA Photographic Collection, and in Öpik, op cit.
Reproduced in 2004, The Griffin Legacy, Canberra the Nation’s Capital in the 21st Century, National Capital Authority, Canberra.
Reproduced in The Griffin Legacy, op.cit.
Pryor, LD and Banks, JCG, op cit.
Burbidge, NT and Gray, M 1970, Flora of the Australian Capital Territory. ANU Press, Canberra.
NCDC, 1984, The Ecological Resources of the ACT, National Capital Development Commission, Canberra.
Environment ACT, op cit.
Gould, L 2004, Picaree Hill—Integrated Conservation Management Plan, Murrumbateman Landcare Group.
Taylor, M and Day, N 1999, Field Guide to the Birds of the ACT, National Parks Association of the ACT Inc.
Gould, op cit.
Muyt, A, 2006, Stirling Ridge, Yarralumla: Vegetation Survey Methods, Management Issues & Flora and Fauna Species Lists, report
prepared for the National Capital Authority, Canberra (unpublished).
Eddy, D, Mallinson, D, Rehwinkel, R, and Sharp, S 1998 (3rd reprint), Grassland Flora—a field guide for the Southern Tablelands (NSW &
ACT), Crown Copyright.
Environment ACT, op cit.
Rowell, A 1996, Yarramundi Grassland Vegetation Mapping and Management Recommendations. Report to the National Capital Planning
Authority. Canberra: ANUTECH Pty Ltd.
Lake Burley Griffin—Heritage Assessment—Final Report, October 2009