Constraining eruption timing and duration at Taranaki volcano, New Zealand, using Late Holocene stalagmites

Abstract

Robust hazard assessment at dormant stratovolcanoes requires high-resolution eruption chronologies, yet these are often limited by incomplete proximal deposits and poorly constrained ages. Speleothems can preserve tephra particles and volcanogenic trace element signals datable using high-precision 230 Th/U chronologies. However, accurate eruption timings are affected by transfer delays of volcanogenic signals in distal cave systems beneath thick epikarst. Here, we investigate Late Holocene (1094 AD –recent) stalagmites from a shallow cave proximal to Taranaki volcano (New Zealand), where cave geometry and location along the primary tephra dispersal axis provide an opportunity to test whether primary tephra preservation improves reconstruction of eruption timing and duration. Laser-induced breakdown spectroscopy mapping of Si, K, and Ti identified several particle-rich layers, of which two comprise pristine tephra based on clustered glass and titanomagnetite compositions as well as grain morphologies indicating narrow grain-size distributions and increased particle angularity. These incorporated tephra particles correspond to the Te Popo and Burrell episodes and were dated using 230 Th/U at 1196 AD ± 31 and 1568 AD ± 41, respectively. Each tephra layer comprises three distinct tephra-rich laminae, indicating multiple eruption pulses. Growth rates across tephra-bearing laminae indicate eruptive pulses lasted several months and were separated by short repose periods, suggesting that each episode lasted around 2.5 years. Particle-rich layers deposited in the late nineteenth–twentieth centuries contain non-volcanic detritus and heterogeneous grains, consistent with dust and soil-derived material mobilised during landscape modification. These results demonstrate that proximal speleothems can be used to improve volcanic hazard assessments by providing precise information on the timing and duration of volcanic eruptions.

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