Human populations and infrastructure in high mountain regions are
exposed to a wide range of natural hazards, the frequency, magnitude,
and location of which are extremely sensitive to climate change. In
cases where several hazards can occur simultaneously or where the
occurrence of one event will change the disposition of another,
assessments need to account for complex process chains. While process
chains are widely recognized as a major threat, no systematic analysis
has been undertaken. We therefore assemble a broad set of process chain
events from across the globe to establish new understanding on the
factors that directly trigger or alter the disposition for subsequent
events in the chain. Based on this new understanding, we derive a novel
classification scheme and parameters to aid natural hazard assessment.
Most process chains in high mountains are commonly associated with
glacier retreat or permafrost degradation. Regional differences exist in
the nature and rate of sequencing---some process chains are almost
instantaneous, while other linkages are delayed. Process chains
involving rapid sequences are difficult to predict or mitigate, and
impacts are often devastating. We demonstrate that process chains are
initialized most frequently as threshold failures, being the result of
gradual landscape weakening and not due to the occurrence of a distinct
trigger. The co-occurrence of fluvial processes or activation of
sediment deposition areas increases the reach of process chains. Climate
change is therefore expected to increase the reach of events in the
future, as glacial environments transform into sediment-rich paraglacial
and fluvial landscapes.