Soil Formation on old coal ash!
Recently, whilst working in a mining area near Dubbo doing some soil mapping work, I came across something which I have only seldom seen before and I don’t think many people would have considered possible. Sticking out of the generally flat surface of the plain was a large mound about 5 – 8 m high and 1 – 2 Ha in area. The mound was covered in grey box vegetation with a sparse shrub understory with some colonising weeds in other more disturbed areas.
The soil that this mound was made of was formed from fly ash, or ash from burned coal from a former ore processing plant nearby. Over many years the ash had been dumped to form the mound and at a guess this stopped in the 1920’s or 30’s after nearly 100 years of operation. Ash is pretty nasty stuff by itself. It is highly alkaline for one thing, with a pH sometimes greater than 12. It is also very silty making it spewy when wet, or like cement when dry. Nonetheless, time and water and native vegetation had made use of this material to form soil of a type. In terms of an Australian Soil Class, it is a Cumulic Anthroposol. Not very meaningful. The fact that this material which actually can burn your hands when mixing it with water, can play host to bacteria, fungi and plants is a testament to how tough soil life really can be.
I hope that you enjoy the photos.
Photo 1: Mound of ash showing wombat and rabbit burrows and well-developed native vegetation.
Photo 2: Cumulic Anthroposol developed on fly ash. Note that there are almost no roots below the top 15 cm because the material is highly caustic.