I am posting two videos that I used to analyze the footage of the dam collapse of the Vale Córrego do Feijão Dam I in Brumadinho. These videos could help others who are trying to analyze the footage for useful information in assessing the collapse. The first video is a closeup slice sequence of the crest or ridge line (in 5 sections from left side of the dam at top to right side at the bottom) showing the initial moments of the failure. The downward progression of the crest line reveals that initial movement occurred just to the left of the drill rig with secondary movements along the crest to either side.
Still, I hope the videos that I am posting here -- and which I had also used to complete my original analysis of the televised footage per the prior post -- can help others with an improved understanding of the slide movement in their assessments of the failure mechanisms involved in the collapse.
The second video shows the entire dam (unlike the video I included in the earlier post that focused on a closeup of the dam's right side where the critical sliding features were located). Circled are the visible areas of the dam where more than one separate instance of movement within the first second of the footage can be detected using extreme closeup analysis of pixels. There are other areas of movement as well, but these are either cloud shadows moving down the face of the dam or video pixelation effects from the source camera feed and/or file compression/conversion.
All apparent movements in dam features (crest, bench, toe, etc.) only occur a single time within the first second of footage other than the two circled areas at the crest and toe of the dam. There are also two cloud shadows (one to the left, one to the right) at the crest of the dam that are moving down the face at the moment of collapse. The two circled areas were discussed in my previous analysis as possibly being involved in the triggering event of the collapse. Conversely, the single instances of movement on the dam within the first second of footage are most likely pixelation or other video effects. I loop the first second at full speed 10 times to better show the dam movement vs. cloud shadows vs. pixelation and then I loop it 5 more times at 0.25x speed as well.
All apparent movements in dam features (crest, bench, toe, etc.) only occur a single time within the first second of footage other than the two circled areas at the crest and toe of the dam. There are also two cloud shadows (one to the left, one to the right) at the crest of the dam that are moving down the face at the moment of collapse. The two circled areas were discussed in my previous analysis as possibly being involved in the triggering event of the collapse. Conversely, the single instances of movement on the dam within the first second of footage are most likely pixelation or other video effects. I loop the first second at full speed 10 times to better show the dam movement vs. cloud shadows vs. pixelation and then I loop it 5 more times at 0.25x speed as well.
This all may seem like a minor detail but I've noted a number of credible sources that might be misinformed about the initial movement and collapse sequence. For example, the non-profit World Mine Tailings Failures states on its blog in an otherwise excellent analysis:
"Finally, we present an analysis of a series of Google Earth images over a period of six years by Frederico Lopes Freire, which shows increasing saturation from constant natural drainage, which was not being diverted or captured, and which flowed into and over the TSF. Freire notes a deformation in the upper left face of the dam where, in our view, the collapse initiated, based on hundreds of loops of our banner. The first indication is a large cloud of black dust right behind this deformation. Three small areas of black dust appeared in the lower right immediately after this first appearance of dust in the upper left. According to Dr. Rodríguez Pacheco, saturation is a key pre-condition for static liquefaction, with 80% being a critical level.
The image below is the exact moment that the first crack appeared in the upper left of the top layer of the dam. This is the area where Freire’s interpretation of the Google Earth images shows increasing saturation. Simultaneously, a large circular area in the front of the lower dam cracks. This area is also emphasized in Freire’s analysis of his Google Earth images, which shows collapse of the main drain leading from the center top to the foot of the original starter dam. For the pre-failure period, Freire’s images show erosion all the way down the face. A 2017 periodic safety review shows massive erosion at and above the toe of the starter dam."
[emphasis mine]As the videos I am posting here demonstrate, there were no initial cracks or "black dust" in the upper left area of the dam. There were in fact cumulus clouds overhead and these clouds cast shadows on the crest and face of the dam. It is unfortunate that these cloud shadows obscured some of the movement especially as they drifted in the same direction as the slide progressed (toward the viewer). It is also too bad that we don't have the original camera footage as some of the video pixelation effects that might be mistaken for slide movement are probably the result of the footage being converted and compressed for the television news broadcast.
Still, I hope the videos that I am posting here -- and which I had also used to complete my original analysis of the televised footage per the prior post -- can help others with an improved understanding of the slide movement in their assessments of the failure mechanisms involved in the collapse.
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