The form of a landscape reflects the interaction of geomorphic processes and their driving environmental conditions, which vary across space and time. These interactions can be complicated by thresholds for the initiation of landscape change and the variability and sequencing of past geomorphic events. Thresholds can modulate the sensitivity of geomorphic processes to the frequency, magnitude, and sequencing of a particular forcing and thereby filter the environmental signals that shape landscapes. In extreme cases, only the largest infrequent disturbances or extreme events initiate change and drive landscape evolution.

We welcome field, experimental, theoretical, and modeling efforts focused on the determination and characterization of thresholds and variability and their relevance across landscapes. We encourage the submission of studies spanning a range of spatial and temporal scales, from single events occurring at the grain scale to landscape-scale observations that integrate geomorphic response over geologic time.