To what extent can we treat topographic metrics such as river long profiles as a long-term record of multiple extreme geomorphic events, and hence use them for hazard prediction? We demonstrate that in an area of rapid mountain erosion where the landscape is highly reactive to extreme events, channel steepness measured by integrating area over upstream distance (chi-analysis) can be used as an indicator of geomorphic change during flash-floods. We compare normalised channel steepness to the impact of devastating floods in the upper Ganga Basin in Uttarakhand, northern India in June 2013. The pattern of sediment accumulation and erosion is broadly predictable from the distribution of normalised channel steepness; in reaches of high steepness, channel lowering up to 5 m undercut buildings causing collapse; in low steepness reaches, channels aggraded up to 30 m and widened causing flooding and burial by sediment. Normalised channel steepness provides a first-order prediction of the signal of geomorphic change during extreme flood events. Sediment aggradation in lower gradient reaches is a predictable characteristic of floods with a proportion of discharge fed by point sources such as glacial lakes. .