Soil/Landform Unit 33

Steep low cones of Black Hill

Area:

349 ha

0.03% of CMA region

The steep low cones in the Gordon-Millbrook area (Hopwoods, Black and O’Donnell Hill) are derived from

basalt, scoria and tuff. These low cones are some of the many eruption points of the Western Uplands that includes many scoria and lava cones to the north. Slopes of these low cones can be quite steep and therefore can be limited in land use. Vegetation communities includes Scoria Cone Woodland, Plains Grassy Woodland and Herb-rich Foothill Forest, most of which is located on O’Donnell Hill. Soils consist of

friable

red gradational soils that are shallow on the crests and upper slopes then become deeper and darker red on mid and lower slopes. With an average annual rainfall of 900 mm, land use is only limited by excessive slopes and possible waterlogging in excessively wet seasons.

Compaction

of these red gradational soils, especially with high traffic conditions (e.g. horticulture), can be managed with controlled traffic and supplementation of soil

organic

matter.

Land unse includes grazing (mainly for fat lamb production) and horticulture
	South western slope of Black Hill

Component	1	2	3	4
Proportion of soil-landform unit	50%	17%	17%	16%
CLIMATE Rainfall (mm)	Annual: 890
Temperature (^oC)	Minimum 6, Maximum 16
Precipitation less than potential evapotranspiration	November-March
GEOLOGY Age and lithology	Pleistocene basalt, scoria, tuff
Geomorphology	2.1.4 Dissected Western Uplands associated with volcanic landforms
LANDUSE	Uncleared: Nature conservation Cleared: Cropping; sheep and cattle grazing; horticulture (including potatoes); residential development
TOPOGRAPHY Landscape	Steep low cones
Elevation range (m)	550-692
Local relief (m)	60
Drainage pattern	-
Drainage density (km/km²)	<0.1
Landform	Volcanic cone		Undulating plain
Landform element	Slope and crest	Crest and upper slope	Mid slope	Unconsolidated sediments
Slope and range (%)	20 (5-40)	4 (1-6)	3 (2-7)	1 (1-2)
Slope shape	Straight	Convex	Straight	Concave
NATIVE VEGETATION Ecological Vegetation Class	Scoria Cone Woodland (2.4%), Plains Grassy Woodland (2.3%), Herb-rich Foothill Forest (1.6%)
Dominant species	E. viminalis, E. radiata, E. obliqua
SOIL Parent material	In situ weathered basalt and scaoria	In situ weathered basalt and scoria	In situ weathered basalt and scoria	In situ weathered sandstone and shale
Description (Corangamite Soil Group)	Stony red gradational soil (40/41)	Red gradational soil, fine structure (40)	Dark red gradational soil, fine structure (40)	Mottled brown, black, grey or yellow sodic texture contrast soil, coarse structure (35/37)
Soil type sites	BD5, BD3, SW8	BD5	BD5	SW90, SFS2, SFS5b
Surface texture	Clay loam	Clay loam	Loam	Clay loam
Permeability	High	High	High	Low
Depth (m)	1	2	1.5	1.5
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Steep slopes combined with overland flow cause rill and sheet erosion. Leaching is associated with nutrient decline.	Steep slopes combined with overland flow cause rill and sheet erosion. Leaching is associated with nutrient decline.	Steep slopes combined with overland flow cause rill and sheet erosion. Leaching is associated with nutrient decline. Soil compaction will benefit from addition of organic matter.	Soils tend to have a low permeability with hardsetting surfaces. Waterlogging and compaction also occur.

Page top