Soil/Landform Unit 108

Volcanic maar situated west of Cobden

Area:

123 ha

0.01% of CMA region

This unit consists of two small maars on the south-western boundary of the catchment, west of Cobden. These small eruptions points within the volcanic Western Plains are surrounded at a lower level by gently undulating basaltic plains. Unit components consist of rises, plains and depressions/craters, which may be water filled. Vegetation of these maar slopes is mainly Herb-rich Foothill Forest. The soils are black texture contrast soils (

Chromosols

) that may have

friable

surfaces with

acidic

upper soils due to the higher rainfall of the area. Land use is intensive grazing (mainly dairying) and some cropping. There is only minor susceptibility to sheet and rill erosion and nutrient decline. Issues such as soil

compaction

and pugging on the less structured soils and waterlogging in the depressions may arise.

This maar near Cobden is now mainly used for grazing and cropping in dry seasons
	The level plain and very low slopes of the maar rim

Component	1	2	3	4
Proportion of soil-landform unit	20%	35%	35%	10%
CLIMATE Rainfall (mm)	Annual: 860
Temperature (^oC)	Minimum 9, Maximum 18
Precipitation less than potential evapotranspiration	October-March
GEOLOGY Age and lithology	Neogene fluvial and marine sediments and Quaternary scoria deposits
Geomorphology	6.1.1 Eruption points of the Volcanic Western Plains
LANDUSE	Uncleared: Nature conservation; water supply; active and passive recreation Cleared: Dairy; cropping; beef cattle and sheep grazing; regional development
TOPOGRAPHY Landscape	Undulating rises
Elevation range (m)	135-155
Local relief (m)	2
Drainage pattern	Annular
Drainage density (km/km²)	0.7
Landform	Rises		Plains	Crater
Landform element	Brown low crests	Mid slopes	Plains	Maar
Slope and range (%)	4 (0-10)	3 (1-10)	1 (0-1)	0 (0-5)
Slope shape	Convex	Convex	Straight	Concave
NATIVE VEGETATION Ecological Vegetation Class	Herb-rich Foothill Forest (1%)
SOIL Parent material	Scoria, ash, basalt	Scoria, ash, basalt	Colluvium, scoria, ash	Scoroa, ash, basalt
Description (Corangamite Soil Group)	Acidic black and mottled black texture contrast soils (37/15)	Acidic black and mottled black texture contrast soils (37/15)	Acidic black and mottled black texture contrast soils (37/15)	Black cracking clays (39)
Soil type sites	SFS5b, SW48, SW25	SFS5b, SW48, MM5109	SFS5b, SW48, MM5109	SW101, SFS2, SW102
Surface texture	Fine sandy clay loam	Fine sandy clay loam, sandy loam	Fine sandy clay loam, sandy loam	Light clay
Permeability	High	High	Moderate	High
Depth (m)	<2	<2	<2, >2	<2, >2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Texture contrast, moderate to high water holding capacity and nutrient holding capacity depending on depth and stoniness. Non-sodic (moderate structure) and slightly acidic subsoils. Moderately rapid site drainage. Some susceptibility to sheet and rill erosion.	Texture contrast, low to moderate water holding capacity and nutrient holding capacity depending on depth and stroniness in upper soil, high in subsoil. Non-sodic (moderate structure) and slightly sodic subsoils. Moderate site drainage. Some susceptibility to nutrient decline and sheet and rill erosion.	Texture contrast, low to moderate water holding capacity and nutrient holding capacity depending on depth and stoniness in upper soil, high in subsoil. Non-sodic (moderate structure) and slightly sodic subsoils. Slow site drainage. Some susceptibility to nutrient decline and sheet and rill erosion.	Uniform expansive clays, high to very high water holding capacity and nutrient holding capacity depending on depth and stoniness. Sodic subsoils, surface soils may be self-mulching. Very low site drainage. Susceptibility to waterlogging.

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