Aso Caldera significant event volcanic eruption
Eruptions
Aso volcano has been active at intervals of approximately 10–20 years with the most active cone in recorded history being Nakadake located in the center of the caldera. It has been active since the sixth century. Eruptions occurred from November 2014 to May 2015, with two major phreatomagmatic eruptions on September 14, 2015, and October 8, 2016. Eruptive activity occurred on 20 October 2021.Main eruption ages and eruption volume (DRE (dense-rock equivalent) is the equivalent magma eruption volume. The volume of erupted products is much higher):
Aso-1: About 266,000 years ago, erupted 32 km3 (7.7 cu mi) DRE.
Aso-2: About 141,000 years ago, erupted 32 km3 (7.7 cu mi) DRE.
Aso-3: About 130,000 years ago, erupted 96 km3 (23 cu mi) DRE.
Aso-4: About 90,000 years ago, erupted 384 km3 (92 cu mi) DRE  which was at least VEI 7.
Nojiri pumice about 84,000 years ago erupted 1 km3 (0.24 cu mi) DRE.
Kusasenrigahama Pumice from Kusasenrigahama at approximately 30,000 years ago erupted 1 km3 (0.24 cu mi) DRE at VEI 5
Jigoku spa about 8,050 BCE, Ikph2 tephra
Janoo before 5,300 BCE Tephta and scora cone
Nakadake 5,300 to 12,000 BCE tephra falls
near Janoo about 5,300 BCE Akamizu lava flow
Near Ikenokubo about 5,300 BCE tuff ring
Jigoku Onsen 3,000 to 4,400 BCE tephra, Ikph1 tephra
Nakadake 3,000 to 4,400 BCE tephra falls
Nakadake 4,000 to 3,000 BCE tephra falls
Unknown vent near Janoo, 2150 BCE Aso central cone No. 1 pumice, ACP-1 tephra
Kishimadake 2,050 BCE >0.02 km3 (0.0048 cu mi) DME VEI 4, KsS tephra
Nakadake 1,600 to 2,000 BCE tephra falls
Ojodake 1,650 BCE >0.02 km3 (0.0048 cu mi) DME VEI 4, OjS tephra
Komezuka, Kamikomezuka 1,350 BCE tephra 0.05 km3 (0.012 cu mi) DME
Unknown Aso 1270 ± 75 BCE
Western central cones debris avalanche 100 CE to 400 BCE
Nakadake 630 ± 50 BCE tephra falls
Nakadake 440 ± 75 CE N2S tephra fall
See timeline for eruptions in historic written record (KEY-pink if confined to volcano, red tephra fall, magenta human deaths)Tectonics
There are multiple active faults both under the volcano and adjacent on this area of the Amur Plate. The Okinawa Plate collides with the Amur Plate to the south and the Pacific Plate is subducting under both. The caldera is located where two volcanic lines intersect, being those in the Central Kyushu Rift Valley with volcanoes of Mount Yufu, in Oita Prefecture, through the Kuju volcanoes and Aso Caldera, and on to Mount Unzen and line that runs from Aso Caldera to the Kirishima volcanic group, Aira Caldera, Ata Caldera, and on to the Kikai Caldera. The high resolution Bouguer gravity imaging of Kyushu has confirmed the caldera to be piston rather than funnel shaped, as originally proposed, and related to known active faults and in particular the gravity gradient zone of the Aso Caldera is part of the Oita-Kumamoto Tectonic Line (OKTL) gravity gradient zone and this appears to connect with the Japan Median Tectonic Lines gravity gradient zone, strengthening the evidence that the lines are closely related tectonic features.
Landmark event Key happening Pivotal occurrence Momentous incident Notable episode