Counting currents: resolving contradictory records of eruption history created by unsteady pyroclastic density current dynamics

Ignimbrite lithofacies analysis can be used to interpret the number and behaviour of pyroclastic density currents (PDCs) generated during a Plinian eruption, through identification of flow units in the rock record. However, pyroclastic stratigraphic successions are rarely complete and without breaks around a volcano, complicating regional analysis of hiatus markers. This study uses entrachron correlation to reconcile conflicting proximal and distal lithofacies architecture of the 273 ka Poris Formation, Tenerife, to reveal a coherent eruption history. The novel correlation illustrates that hiatus in PDC activity can vary spatially and rapidly due to regional-scale unsteadiness and non-uniformity in PDC dynamics. Distal stratigraphy may not accurately record the number of PDCs generated during an eruption and breaks in ignimbrite deposition do not necessarily imply discontinuous PDC development. These findings bear importantly on hazard inferences derived from ignimbrite lithofacies successions, and have significance for numerical and experimental modelling of unsteadiness in granular flows.