6 September 2021
Catoca mine in Angola – using satellite imagery to understand recent events
According to Wikipedia, Catoca mine in Angola is the fourth largest diamond mine in the world. Located at -9.399, 20.301, it consists of a big open cast pit and a very large tailings storage area.
Last month, CRREBaC released information about a set of very significant pollution events in the rivers of Angola and Congo, linked to mining in Angola. Reports have included the pollution of hundreds of kilometres of the river system, deaths of fish and hippos and, in some cases, suggestions of up to twelve fatalities. Detailed information to evidence these huge losses is lacking, but there is little doubt that serious pollution occurred.
Whilst this blog is about landslides, I have very often written (and indeed campaigned) about the scandalously poor management of tailings in the mining industry, and I have highlighted several major tailings dam failures. My interest in the events in Angola and Congo results from concerns that the events might have been one or more tailings dam collapses.
One of the candidate sites for the events in Angola is the facility at Catoca, and indeed the operators have reportedly admitted that a release did occur, but only of water and sand.
This is a satellite image of the Catoca facility collected by Planet Labs on 21 July 2021:-
The pit is in the bottom right hand corner, the tailings facility in the huge orange area on the left side of the image. The tailings dam is located just above the centre of the image, orientated NNW-SSE. There is no evidence of any problem in this image.
The first sign of change appears in the image of 24 July 2021. The change is subtle but significant:-
I have put a black circle around some clear pollution on the downstream side of the tailings dam. Note that the tailings dam was intact (and remains so). A day later the problems had become very much worse:-
By 25 July 2021 a large plume of pollution had appeared on the downstream side of the tailings dam (highlighted with a circle again). The had entered the watercourse, which was now showing very clear signs of pollution (highlighted with an arrow).
The situation today, a few weeks later, is interesting:-
The plume has developed considerably , although it has not enlarged significantly (black circle). The polluted watercourse is very clear. There is clear evidence of works around the plume (new roads for example) and on the upstream side of the dam (white circle).
From the images above the pollution might not at first sight look serious, but satellite images downstream might tell a different story. This image was collected on 25 July 2021 at about 8:56 UT, downstream of Catoca at -9.127, 20.346:-
The river is flowing from the south to the north. In the lower part of the image the river is bright orange with pollution. In the northern part of the image the river is unpolluted. The marker, at -9.127, 20.346 is the approximate front of the pollution moving downstream from Catoca. Note the profound change in the water as the pollution front moves through.
This is even more profoundly illustrated in the image below. The small tributary from Catoca flows in from the southwest. It meets the main channel, flowing from south to north. Note the huge change in water quality from this point onwards:-
This location is -9.309, 20.362.
In a statement last month, the company admitted that there had been a “rupture in the pipeline that works as a spillway.”
The satellite images are consistent with this as the source of the pollution, although the ecological damage looks to be more severe than some have suggested.
However, there is an anomaly. The CRREBaC report indicates that substantial pollution was first seen in the rivers of Angola from 15 July 2021:
On the basis of the Sentinel images published by Visio Terra (Equipe Sentinel Vision, EVT919, 2021) and our preliminary investigations from riparian communities, this pollution has been observed since 15 July 2021 from the source in the Angola part of the basin and would have taken 15 days to reach the city of Tshikapa, and 21 days for the city of Ilebo in the Democratic Republic of the Congo (DRC).
The pollution observed on 15 July 2021 does not seem to have come from Catoca according to the images, which suggests a second serious event occurred in a different mine in the area.
Planet Team (2021). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/