Weathering Intensity

Weathering intensity or the degree of weathering is an important characteristic of the

earth’s surface that has a significant influence on the chemical and physical properties

of surface materials. Weathering intensity largely controls the degree to which primary

minerals are altered to secondary components including clay minerals and oxides. The

degree of surface weathering is particularly important in Australia where variations in

weathering intensity correspond to the nature and distribution of regolith (weathered

bedrock and sediments) which mantles approximately 90% of the Australian continent. The

weathering intensity prediction has been generated using the Random Forest decision tree

machine learning algorithm. The algorithm is used to establish predictive relationships

between field estimates of the degree of weathering and a comprehensive suite of

covariate or predictive datasets. The covariates used to generate the model include

satellite imagery, terrain attributes, airborne radiometric imagery and mapped geology.

Correlations between the training dataset and the covariates were explored through the

generation of 300 random tree models. An r-squared correlation of 0.85 is reported using

5 K-fold cross-validation. The mean of the 300 models is used for predicting the

weathering intensity and the uncertainty in the weathering intensity is estimated at

each location via the standard deviation in the 300 model values. The predictive

weathering intensity model is an estimate of the degree of surface weathering only. The

interpretation of the weathering intensity is different for in-situ or residual

landscapes compared with transported materials within depositional landscapes. In

residual landscapes, weathering process are operating locally whereas in depositional

landscapes the model is reflecting the degree of weathering either prior to erosion and

subsequent deposition, or weathering of sediments after being deposited. The weathering

intensity model has broad utility in assisting mineral exploration in variably weathered

geochemical landscapes across the Australian continent, mapping chemical and physical

attributes of soils in agricultural landscapes and in understanding the nature and

distribution of weathering processes occurring within the upper regolith.

For service status information, see https://status.dea.ga.gov.au