Complex variations during a caldera-forming Plinian eruption, including precursor deposits, thick pumice fallout, co-ignimbrite breccias and climactic lag breccias

the 184 ka Lower Pumice 1 eruption sequence, Santorini, Greece

Jack Michael Simmons, Raymond Cas, T. H. Druitt, Christopher Folkes

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The 184 ka Lower Pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases: (1) a minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C). The precursor phase produced 13 small-volume pyroclastic fallout, surge and flow deposits, which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style, and exhibit a normal (dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite) compositional zonation of juvenile pyroclasts in the stratigraphy. Incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main Plinian eruption phase. The Plinian magmatic eruption phase is defined by three major stratigraphic divisions, including a basal pumice fallout deposit (LP1-A), an overlying valley-confined ignimbrite (LP1-B) and a compositionally zoned (rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which caps the sequence. This sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late-stage caldera collapse events. Similarities in pyroclast properties (i.e., chemistry, density), between the Plinian fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the LP1 eruption. Conversely, lithic breccias at the base of the LP1-B ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and/or the initiation of caldera collapse, leading to vent widening, an increase in magma discharge rate and the increased incorporation of lithics into the eruption column, causing mass overload. Lithic-rich lag breccia deposits (LP1-C), which cap the eruption sequence, record incremental, high-energy caldera collapse events, whereby downfaulting occurred in discrete jumps, resulting in variable magma discharge rates and the development of a fissure vent system.

Original languageEnglish
Pages (from-to)200-219
Number of pages20
JournalJournal of Volcanology and Geothermal Research
Volume324
DOIs
Publication statusPublished - 15 Sep 2016

Keywords

  • Collapse breccias
  • Ignimbrite
  • Lower Pumice 1 (LP1)
  • Plinian eruption
  • Precursory eruption
  • Santorini caldera

Cite this

@article{51b8db04431c4c0589c1d18e2a51bcbb,
title = "Complex variations during a caldera-forming Plinian eruption, including precursor deposits, thick pumice fallout, co-ignimbrite breccias and climactic lag breccias: the 184 ka Lower Pumice 1 eruption sequence, Santorini, Greece",
abstract = "The 184 ka Lower Pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases: (1) a minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C). The precursor phase produced 13 small-volume pyroclastic fallout, surge and flow deposits, which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style, and exhibit a normal (dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite) compositional zonation of juvenile pyroclasts in the stratigraphy. Incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main Plinian eruption phase. The Plinian magmatic eruption phase is defined by three major stratigraphic divisions, including a basal pumice fallout deposit (LP1-A), an overlying valley-confined ignimbrite (LP1-B) and a compositionally zoned (rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which caps the sequence. This sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late-stage caldera collapse events. Similarities in pyroclast properties (i.e., chemistry, density), between the Plinian fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the LP1 eruption. Conversely, lithic breccias at the base of the LP1-B ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and/or the initiation of caldera collapse, leading to vent widening, an increase in magma discharge rate and the increased incorporation of lithics into the eruption column, causing mass overload. Lithic-rich lag breccia deposits (LP1-C), which cap the eruption sequence, record incremental, high-energy caldera collapse events, whereby downfaulting occurred in discrete jumps, resulting in variable magma discharge rates and the development of a fissure vent system.",
keywords = "Collapse breccias, Ignimbrite, Lower Pumice 1 (LP1), Plinian eruption, Precursory eruption, Santorini caldera",
author = "Simmons, {Jack Michael} and Raymond Cas and Druitt, {T. H.} and Christopher Folkes",
year = "2016",
month = "9",
day = "15",
doi = "10.1016/j.jvolgeores.2016.05.013",
language = "English",
volume = "324",
pages = "200--219",
journal = "Journal of Volcanology and Geothermal Research",
issn = "0377-0273",
publisher = "Elsevier",

}

TY - JOUR

T1 - Complex variations during a caldera-forming Plinian eruption, including precursor deposits, thick pumice fallout, co-ignimbrite breccias and climactic lag breccias

T2 - the 184 ka Lower Pumice 1 eruption sequence, Santorini, Greece

AU - Simmons, Jack Michael

AU - Cas, Raymond

AU - Druitt, T. H.

AU - Folkes, Christopher

PY - 2016/9/15

Y1 - 2016/9/15

N2 - The 184 ka Lower Pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases: (1) a minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C). The precursor phase produced 13 small-volume pyroclastic fallout, surge and flow deposits, which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style, and exhibit a normal (dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite) compositional zonation of juvenile pyroclasts in the stratigraphy. Incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main Plinian eruption phase. The Plinian magmatic eruption phase is defined by three major stratigraphic divisions, including a basal pumice fallout deposit (LP1-A), an overlying valley-confined ignimbrite (LP1-B) and a compositionally zoned (rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which caps the sequence. This sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late-stage caldera collapse events. Similarities in pyroclast properties (i.e., chemistry, density), between the Plinian fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the LP1 eruption. Conversely, lithic breccias at the base of the LP1-B ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and/or the initiation of caldera collapse, leading to vent widening, an increase in magma discharge rate and the increased incorporation of lithics into the eruption column, causing mass overload. Lithic-rich lag breccia deposits (LP1-C), which cap the eruption sequence, record incremental, high-energy caldera collapse events, whereby downfaulting occurred in discrete jumps, resulting in variable magma discharge rates and the development of a fissure vent system.

AB - The 184 ka Lower Pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases: (1) a minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C). The precursor phase produced 13 small-volume pyroclastic fallout, surge and flow deposits, which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style, and exhibit a normal (dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite) compositional zonation of juvenile pyroclasts in the stratigraphy. Incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main Plinian eruption phase. The Plinian magmatic eruption phase is defined by three major stratigraphic divisions, including a basal pumice fallout deposit (LP1-A), an overlying valley-confined ignimbrite (LP1-B) and a compositionally zoned (rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which caps the sequence. This sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late-stage caldera collapse events. Similarities in pyroclast properties (i.e., chemistry, density), between the Plinian fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the LP1 eruption. Conversely, lithic breccias at the base of the LP1-B ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and/or the initiation of caldera collapse, leading to vent widening, an increase in magma discharge rate and the increased incorporation of lithics into the eruption column, causing mass overload. Lithic-rich lag breccia deposits (LP1-C), which cap the eruption sequence, record incremental, high-energy caldera collapse events, whereby downfaulting occurred in discrete jumps, resulting in variable magma discharge rates and the development of a fissure vent system.

KW - Collapse breccias

KW - Ignimbrite

KW - Lower Pumice 1 (LP1)

KW - Plinian eruption

KW - Precursory eruption

KW - Santorini caldera

UR - http://www.scopus.com/inward/record.url?scp=84975824114&partnerID=8YFLogxK

UR - http://ac.els-cdn.com.ezproxy.lib.monash.edu.au/S037702731630107X/1-s2.0-S037702731630107X-main.pdf?_tid=ef8204f8-db9f-11e6-b90b-00000aacb361&acdnat=1484539244_e6488654a81926b5ab001a82afe51628

U2 - 10.1016/j.jvolgeores.2016.05.013

DO - 10.1016/j.jvolgeores.2016.05.013

M3 - Article

VL - 324

SP - 200

EP - 219

JO - Journal of Volcanology and Geothermal Research

JF - Journal of Volcanology and Geothermal Research

SN - 0377-0273

ER -