How Do Equity Markets Price Disaster Risk? Evidence from Vale after the Mariana Disaster

This study examines how the Fundão tailings dam collapse (Mariana, Brazil) was priced in Vale S.A.’s equity returns, and whether the observed dynamics are consistent with rapid adjustment under the Efficient Market Hypothesis (EMH) when the shock has ‘black swan’ features. We apply the synthetic control method to construct a transparent counterfactual path for Vale’s semiannual cumulative stock returns over 2011.2-2017.2. To address potential spillovers and comparator contamination, we estimate three donor-pool specifications: DP1 (Brazilian and international peers), DP2 (excluding Brazilian firms), and DP3 (excluding Brazilian firms and BHP Group). DP1 delivers the strongest pre-disaster fit and is adopted as the baseline. The results show a negative return response in the disaster semester (2015.2), consistent with an immediate shock, but the most informative pattern arises afterward: Vale underperforms its synthetic counterfactual persistently in 2016.1-2017.2. This sustained post-event gap suggests delayed market adjustment as legal, regulatory, and reputational uncertainties unfold beyond the initial news window. Placebo-style comparisons support the interpretation that Vale’s post-disaster divergence is not a mere artifact of random fluctuations under strong pre-event fit. Overall, the study contributes to disaster finance by providing firm-level evidence on the persistence of disaster-related repricing and by highlighting governance, transparency, and disaster-risk management as relevant mechanisms for limiting valuation losses under extreme events. JEL classification: G14; Q54; Q56; L72; C23