Geological study of phreatic eruptions

Abstract

Phreatic (non-juvenile) eruptions are the most common type of magmatic activity on Earth. Here we review the characteristics of phreatic eruptions, which occur when overheated water is rapidly vaporized. Tephra layers produced by phreatic eruptions are composed mainly of clay-rich volcanic ash with variably altered lapilli and volcanic blocks. A single phreatic eruption can last between one hour and one day; however, eruptions may occur successively over a period of years to decades. The total volume of tephra produced by a phreatic eruption is typically -m , maximum < m . Phreatic eruptions may be accompanied by diverse phenomena, including: tephra fallout, ejected rock fragments, low-temperature pyroclastic flows, and syneruptive-spouted type lahars. There are few detailed descriptions of low-temperature (~ °C ) pyroclastic flows and syneruptive-spouted type lahars associated with phreatic eruptions. Detailed studies of phreatic phenomena are required, as it remains difficult to identify and reconstruct these processes based on the characteristics of the deposits.

Tephra-stratigraphy and Ash Componentry Studies of Proximal Volcanic Products at Mount Tangkuban Parahu, Indonesia: An Insight to Holocene Volcanic Activity

“…Phreatic deposits are mostly identified from a field observation, presented as white and yellow colour tephra succession with a range of grain size from ash to block fragment (Maeno et al, 2016;Oikawa et al, 2018). There are also an increasing number of studies using componentry analysis of volcanic products to classify phreatic explosion from phreatomagmatic eruption (e.g., Pardo et al, 2014;Suzuki et al, 2013;Alvarado et al, 2016).…”

“…Their emplacement is mostly associated with the lapilli to block-sized lithic fragments (e.g., pyroclastic breccia; upper composite stratigraphy). Their concentration decreases toward to distal area (<1.5 km) (i.e., Unit 2, Unit 3), which is very common for the volcanic products from the low-explosive intensity (e.g., Maeno et al, 2016;Oikawa, 2018). However, it is still challenging to understand their emplacement process (e.g., fall-out, flow) due to the limited observed locations and mostly closed the sourced-vent (Ratu crater).…”

Quantitative relationship between plume emission and multiple deflations after the 2014 phreatic eruption at Ontake volcano, Japan

“…Phreatic eruptions occur frequently on volcanoes around the world. Despite their frequency, the triggering mechanisms and subsurface conditions leading to phreatic eruptions have not been well understood (Barberi et al 1992;Oikawa et al 2018). Germanovich and Lowell (1995) proposed a conceptual model suggesting that phreatic eruptions result from pressurization in volcanic, hydrothermal systems due to the injection of hot fluids from the magmatic region.…”

Special issue “Towards forecasting phreatic eruptions: examples from Hakone volcano and some global equivalents”

“…A recent extensive review counted 116 phreatic eruptions of 36 volcanoes during the period from 1900 to 2015 (approximately one per year on average) in Japan, which has very detailed records of volcanic eruptions (Oikawa et al 2018). However, few of these eruptions had interested volcanologists probably because limited ash dispersal and geophysical observations did not allow detailed analysis.…”