Revisiting the lacquer peels method with pyroclastic deposits: Sediment plates, a precise, fine scale imaging method and powerful outreach tool

Pyroclastic sedimentary successions record an eruptive history modulated by transport and depositional phases. Here, a field technique of outcrop impregnation was used to document pyroclastic sediments at the scale of individual laminae. The details so obtained have the potential to reveal new insights into the dynamics of transport and deposition of pyroclastic currents and fallout. Sediment plates (a type of lacquer peels) represent a sampling method whereby a thin plate of undisturbed sediments is obtained directly from the outcrop. A low-viscosity, hardening epoxy resin is applied to a freshly exposed cross-section of an unconsolidated deposit and impregnates a surface layer of the cross-section via capillary forces before solidifying. Upon hardening, a solid plate (0.5-5cm thick and up to 2m in length) of the sedimentary formation can be recovered and transported with full preservation of the initial organization of the particles. Sediment plates are capable of recording and highlighting details of stratification to a very fine scale and high degree of precision. This method represents a valuable tool for research, education, and exhibition purposes. A dataset of 50m² of sediment plates was created from the primary sedimentary structures emplaced during 1) the August 2006 eruption of Tungurahua volcano (Ecuador), 2) the Laacher See eruption (Germany) and 3) Astroni surge deposits (Campi Flegrei, Italy). This dataset has been put to use in several contexts: 1) analysis of sedimentation processes at the boundary-layer scale, 2) data comparison with remote measurements (e.g., ground penetrating radar), 3) archiving and conservation, 4) as teaching material and 5) for dissemination exercises during exhibition in museums.