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[SCG54-P04] The Life of Submarine Caldera Volcanoes in Oceanic Arcs – A Hypothesis
Keywords:Submarine volcano, Caldera volcano, Caldera-forming eruption
A submarine caldera volcano is a significant biological hotspot, an outstanding prospect for mineral exploration, and a serious volcanic hazard to human society. In recent decades, an increasing number of calderas in the modern world have been explored, allowing us to witness the snapshots of the life of submarine caldera volcanoes. With the knowledge from such calderas in the geological past bridged by recent observations, it is now possible to hypothesise the entire life of submarine calderas in oceanic arcs, which has a great environmental, economic, and hazardous impact.
The life of a future submarine caldera in an oceanic arc may start with either the migration of a new subduction zone or the rapid subsidence of a preexisting arc influenced by a back-arc opening. The seafloor in such nascent environments typically ranges between 1000 to 2500 m depth, which is too deep for magma to fragment explosively due to the hydrostatic pressure. Initially, the volcanism is mostly limited to effusive activity, which is highly constructive for the volcano’s edifice. Lava flow and hyaloclastites dominate its geological succession in this “Growing” period. Typical modern examples are the submarine volcanoes in the southern Kermadec arcs.
Upon reaching a depth of 1000 meters and potentially establishing a mature magma chamber, the volcano enters a phase of accelerated magma eruption. This intensification could stem from the expansion of a substantial magma chamber or the catastrophic disintegration of a pre-existing edifice due to the explosive fragmentation of magma. At this juncture, the volcano undergoes its first caldera-forming eruption, predominantly ejecting pumice clasts as it largely transpires below the magma's fragmentation depth. Resultantly, the initial caldera emerges as a relatively compact, nearly symmetrical, and profound formation. During this nascent "Young" stage, the edifice's growth decelerates, which is attributed to the inefficacy of pumice in constructing a voluminous structure. Contemporary instances that epitomise this phase include Myojin Knoll in the Izu arc and Brothers Caldera in the Kermadec arc, serving as archetypal illustrations of such youthful submarine volcanic activity.
Upon reaching a more superficial depth of approximately 500 meters, the volcano undergoes a series of transformative caldera-forming eruptions. At this “Mature” stage, the diminished hydrostatic pressure allows for the explosive fragmentation of magma, leading to the eruption of substantial ignimbrite volumes akin to those observed in subaerial calderas. This marks the transition of the caldera to a polygenetic stage, characterised by intricately shaped rims, a shallow sedimentary basin replete with intra-caldera deposits, and a vast edifice gently sloped by accumulated ignimbrite layers. In this mature phase, fluctuations in sea level play a pivotal role in modulating both volcanic activity and the morphological evolution of the landscape. Notable examples of such mature submarine calderas include Sumisu in the Izu arc and Macauley in the Kermadec arc, each showcasing the intricate interplay between geological processes and marine environments.
The lifecycle of a submarine caldera volcano within an arc concludes as regional tectonic dynamics shift. Such transformations may arise from alterations in plate motion or the cessation of back-arc rifting/spreading, acting as catalysts for the “Fossilising” phase. This tectonic evolution leads to a diminished influx of magma beneath the volcano, precipitating the crystallisation of the vast magma chamber and heralding a relatively swift cessation of volcanic activity. Subsequently, the caldera may temporarily assume the role of a shallow sedimentary basin. Over geological timescales, the now extinct oceanic arc may collide with a continent or another arc, thereby becoming fossilised within the geological record.
The life of a future submarine caldera in an oceanic arc may start with either the migration of a new subduction zone or the rapid subsidence of a preexisting arc influenced by a back-arc opening. The seafloor in such nascent environments typically ranges between 1000 to 2500 m depth, which is too deep for magma to fragment explosively due to the hydrostatic pressure. Initially, the volcanism is mostly limited to effusive activity, which is highly constructive for the volcano’s edifice. Lava flow and hyaloclastites dominate its geological succession in this “Growing” period. Typical modern examples are the submarine volcanoes in the southern Kermadec arcs.
Upon reaching a depth of 1000 meters and potentially establishing a mature magma chamber, the volcano enters a phase of accelerated magma eruption. This intensification could stem from the expansion of a substantial magma chamber or the catastrophic disintegration of a pre-existing edifice due to the explosive fragmentation of magma. At this juncture, the volcano undergoes its first caldera-forming eruption, predominantly ejecting pumice clasts as it largely transpires below the magma's fragmentation depth. Resultantly, the initial caldera emerges as a relatively compact, nearly symmetrical, and profound formation. During this nascent "Young" stage, the edifice's growth decelerates, which is attributed to the inefficacy of pumice in constructing a voluminous structure. Contemporary instances that epitomise this phase include Myojin Knoll in the Izu arc and Brothers Caldera in the Kermadec arc, serving as archetypal illustrations of such youthful submarine volcanic activity.
Upon reaching a more superficial depth of approximately 500 meters, the volcano undergoes a series of transformative caldera-forming eruptions. At this “Mature” stage, the diminished hydrostatic pressure allows for the explosive fragmentation of magma, leading to the eruption of substantial ignimbrite volumes akin to those observed in subaerial calderas. This marks the transition of the caldera to a polygenetic stage, characterised by intricately shaped rims, a shallow sedimentary basin replete with intra-caldera deposits, and a vast edifice gently sloped by accumulated ignimbrite layers. In this mature phase, fluctuations in sea level play a pivotal role in modulating both volcanic activity and the morphological evolution of the landscape. Notable examples of such mature submarine calderas include Sumisu in the Izu arc and Macauley in the Kermadec arc, each showcasing the intricate interplay between geological processes and marine environments.
The lifecycle of a submarine caldera volcano within an arc concludes as regional tectonic dynamics shift. Such transformations may arise from alterations in plate motion or the cessation of back-arc rifting/spreading, acting as catalysts for the “Fossilising” phase. This tectonic evolution leads to a diminished influx of magma beneath the volcano, precipitating the crystallisation of the vast magma chamber and heralding a relatively swift cessation of volcanic activity. Subsequently, the caldera may temporarily assume the role of a shallow sedimentary basin. Over geological timescales, the now extinct oceanic arc may collide with a continent or another arc, thereby becoming fossilised within the geological record.