We propose a new methodology to describe and detect price reversals. We highlight
the benets of our method compared to classic measures of transient market ineciency,
such as the variance ratio. We show that (i) our characterization is consistent with the
forensic denition used by the SEC in legal charges for market access rule violation causing
ash crashes, (ii) recent years have seen an increase in the frequency and severity of mini-
ash crashes, and (iii) transient ineciencies are not necessarily short-lived, and imply
signicant wealth redistribution when coupled with frictions such as a supply shock.