Abstract
Mt Ruapehu is one of New Zealand’s most active volcanoes, last erupting in 2007. Few studies have investigated the pyroclastic density current (PDC) occurrence on this volcano, despite PDCs being one of the most hazardous volcanic processes. Poor preservation of PDC deposits, due to past glaciations, erosion, burial, and poor consolidation has left a significant gap in Mt Ruapehu’s eruptive record. By identifying and characterising PDCs on Mt Ruapehu this paper provides an updated account of PDC occurrence on this volcano. Comprehensive field-mapping forms the basis for this study by identifying PDC deposits from partial outcrop exposures. We use field observations of these deposits to describe the lithofacies and infer PDC behaviour. Relative stratigraphy and whole-rock geochemistry are used to correlate deposits with dated units from literature and provide approximate age ranges. This study found 12 PDC deposits representing at least 10 previously unidentified flows. Combined with PDCs identified in previous studies there is a total of 23 PDC deposits found on Mt Ruapehu, including the PDC observed during the 1945 eruption. These PDCs have been emplaced throughout Mt Ruapehu’s 250 ka eruptive history. The PDCs were concentrated and dominated by granular flow or granular fluid-based flow transport regimes. The lithofacies show PDCs forming from column collapse and dome collapse or explosion events. This demonstrates that Mt Ruapehu is capable of producing a spectrum of PDC styles, something that must be considered during future hazard planning on the volcano.
Highlights
With increasing populations, urbanization, and infrastructure over the last 50 years, natural hazards such as volcanic eruptions are posing a greater threat to society (Johnston et al, 2000)
Other potential Pyroclastic density current (PDC) deposits were identified in the field while accessing these targeted areas
We describe the lithofacies for each deposit (Table 2) based on the textural characteristics observed in the field and interpret the PDC behavior based on these facies
Summary
Urbanization, and infrastructure over the last 50 years, natural hazards such as volcanic eruptions are posing a greater threat to society (Johnston et al, 2000). It is crucial to fully understand these hazards in order to reduce the impact they have on society This is especially important at volcanoes with large numbers of tourists, such as Mt. Ruapehu (New Zealand), or numerous residents living in the impact area. PDCs can be generated by several different mechanisms: the collapse of an eruption column, boiling-over (Branney and Kokelaar, 2002), directed lateral blast (Waitt Jr., 1981), explosion or gravitational collapse of a lava dome (Dufek et al, 2015) or the toe of flowing lava (Valentine et al, 2000; Stinton and Sheridan, 2008; Buchwaldt, 2013; Dufek et al, 2015), or the collapse of accumulated Strombolian spatter (Valentine et al, 2000). These different mechanisms can produce different styles and sizes of PDCs
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