Tsunami scour has received increasing attention over the past decade, given its role as a critical failure mode for building damage, and in particular the wide scale damage to infrastructure resulting from the 2004 Sumatra Andaman Tsunami and the 2011 Tohoku Tsunami. This paper uses observed scour from these events to distinguish four primary scour mechanisms: local scour (often associated with pore pressure softening), overtopping scour, channelized scour (in which flow is concentrated in a channel), and general scour or wide area erosion. The first two of these are commonly observed to undercut buildings and other structures. Simple models are presented for these two scour mechanisms correlated to field measurements and observations, providing upper limits on the observed scour depth values. Correlation of scour behavior by soil type, common in theoretical models, is not supported by the present data set, so a general condition is recommended for current practice.