**2. Background of the Brumadinho Tailings Dam Failure Disaster**

Brumadinho is a Brazilian municipality, located near the Paraopeba River at an altitude of 880 m. It belongs to the microregion of Belo Horizonte, Metropolitana de Belo Horizonte, Minas Gerais, Brazil (Figure 1). Just after noon on 25 January 2019, the Brumadinho dam disaster occurred when Dam I (Figures 2 and 3), a tailings dam at the Córrego do Feijão iron ore mine owned by Vale, 9 km (5.6 mi) east of Brumadinho (Figure 1b), suffered a catastrophic failure [13].

**Figure 1.** Location of Brumadinho dam disaster. (**a**) Location of the disaster in Brazil; (**b**) relative relationship between the disaster location and two reservoirs. Note that in Figure 1b, the position of two reservoirs were marked using a red box whose extent corresponds to Figure 9a.

**Figure 2.** Video screenshots of the Brumadinho tailings dam failure [14]; (**a**) 25 January 2019, 12:28:21; (**b**) 25 January 2019, 12:28:36; (**c**) 25 January 2019, 12:28:43; (**d**) 25 January 2019, 12:28:52 (local time).

In this disaster, at least 248 people were confirmed dead, and 22 missing. Most of the victims were Vale's employees. At a railroad branch, in the Córrego do Feijão region, three locomotives and 132 wagons were buried, and four railway men were missing. Two sections of the railway bridge (Figure 3) and about 100 m of railway track were also struck and destroyed by the mud [15]. Due to the potential hazards, about 24,000 residents from several districts of Brumadinho were evacuated [16]. Many agricultural areas were affected or totally destroyed, and the local livestock industry suffered damages due to the loss of animals such as cattle and poultry [17]. In addition, the tailings dam failure spilt about 12 million cubic meters of mud and sludge [18] and some came into and ran along the

Paraopeba River. The metals in the tailings may be adsorbed by the river sediments or may pollute the soil in the floodplain, and would end up affecting the region's ecosystem.

**Figure 3.** Disaster pictures. (**a**) Aerial view of Brumadinho dam disaster taken at 11:46 on 27 January 2019 [19]; (**b**) video screenshot of the destroyed railway bridge, 3 km downstream from the collapsed dam, on 26 January 2019 from YouTube [20]; (**c**) picture of iron ore railway bridge destroyed by mudflow taken on 26 January 2019 [21]. Note that the yellow line represents the extents of the areas affected by the mudflow, the red line represents the railway bridge which was damaged, and the brown arrow indicates the movement direction of the mudflow.
