Source: Yuri Edmundo/EPA via The New York Times

 

Source: Antonio Lacerda/EPA via The Guardian

 

On January 25th, a dam at the Corrego de Feijão iron ore mining complex in the state of Minas Gerais in Brazil collapsed without warning. Within seconds, an estimated 12 million cubic meters of sludge, mud and debris was carried nearly ten kilometers downhill through valleys, agricultural lands and communities before entering the river system. In some places, eight meters of mud buried homes and other buildings and at the time of writing there were 121 known casualties and 226 missing. Many of those killed were employees of the mine eating lunch in the dining complex, which was buried.

 

While this tragedy occurred ten days ago and multiple examples of basic analyses were shared, PlanetWatchers is hoping to shed more light on the extended aftermath of the dangerous flow of mud as well as provide insights into how the different textures and materials in the mud flowed downhill.

 

As the dam was holding iron ore tailings (the byproducts remaining following the extraction of iron ore, such as rocks and chemicals used in the extraction process), the ‘mud’ was actually a composition of many different liquids and solids. As such, as the mud travelled away from the dam, certain components travelled further than others and settled along different parts of the final route of the flow. PlanetWatchers utilized synthetic aperture radar imagery from Sentinel-1 and optical imagery from Sentinel-2 (both operated by the European Space Agency).

 

PlanetWatchers regularly uses multiple data sources to perform change detection analysis over time as it allows for a variety of spatial and temporal resolutions and additional insights. In this case, using radar imagery allowed for the analysis of differing flows along the route of the mudflow and to highlight locations with finer tailings and locations with a coarser composition, such as larger rocks and debris.

 

Image One shows an optical image side by side of before and after the dam collapse. The left image was acquired on January 22nd and the right image was acquired on February 1st. The extent of damage is clearly visible in the image on the right.

 

Image One: Side by side comparison of optical image (Sentinel-2) showing before and after damage from dam collapse. Left: Image acquired on January 22nd with the dam circled in the top right corner. Right: Image acquired on February 1st showing the same extent as the left image with the affected area outlined.

 

Image Two shows a Sentinel-1 radar image composite of multiple bands on the affected areas of the dam collapse. This image combines two radar images, the first was acquired on January 17th and the second was acquired on January 29th. The blue region highlights areas that were flooded by the dam collapse as of January 29th.

 

Image Two: Synthetic aperture radar composite of two images showing affected areas in blue. The first image was acquired on January 17th and the second image was acquired on January 29th.

 

Image Three overlays the flooded area extracted from the radar composite (in red and orange) on an optical image to highlight the extent of the damage from the dam collapse. Based on the radar analysis we can determine that the northern part of the river (closer to the dam) has more coarse gravel and rocks (red), while the southern part contains finer sediments in a more liquid state (orange). These results are supported by the post-event optical image from Sentinel-2 where we can see different colors at the exact same areas the radar is showing different texture (see Image One on the right).

 

Image Three: Radar composite (red) overlayed on optical image showing the extent of the damaged area from the dam collapse. Red areas are those with more coarse gravel and rocks. Orange areas are those with finer sediments and a higher water content.

 

Moreover, with the post-event Sentinel-2 image from February 1st we were able to measure that the finer sediments have travelled about 50 kilometers to the northwest along the Rio Paraopeba as can be seen in Image Four. These fine sediments are on their way to the São Francisco River near the Três Marias Dam and the municipality of Três Marias that resides about 300 kilometers downstream. Considering the previous rate of sediment progress, the front of the sediment is expected to reach the reservoir formed by the Três Marias Dam by the beginning of March. All three of these images demonstrate the catastrophic event that unfolded less than two weeks ago in Brazil.

Image Four: Sentinel-2 image from February 1st showing the extent of sediment in Rio Paraopeba near Juatuba approximately 50 kilometers downstream from the dam collapse. In the coming weeks, this sediment is expected to reach additional bodies of water, such as the São Francisco River near the Três Marias Dam. Section A shows a stretch of the river that is full of mud and debris from the dam collapse. Section B shows a stretch of the river that was not impacted by sediment as of February 1st.

 

PlanetWatchers performed this analysis in the hopes of assisting in the recovery efforts. We hope these maps help in some way.

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