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Table 4 Type classifications of volcanic ashes from the 2018–2019 eruption at Kuchinoerabujima Volcano

From: Influence of hydrothermal recharge on the evolution of eruption styles and hazards during the 2018–2019 activity at Kuchinoerabujima Volcano, Japan

Type Type-1 Type-2 Type-3
  Non-altered Partially altered Intensely altered
Sub-type    Type 3–1 Type 3–2 Type 3–3 Type 3–4 Type 3–5
Name of particle    Silica Sulfate Sulfide Sulfur-bearing Others
Optical discription -Glassy luster, translucent gray-color to transparent dark-color particles
Angular to sub-angular shape
Translucent gray- to white-color particles
Angular to sub-angular shapes
White-, yellowish brown-, or dark-colored particles
Angular to rounded shapes
X-ray map
(intense elements)
Si, Al, K Si, Al, K Si S, Ca S, Fe S Al, K, Ca
Minerals contained Silica mineral(s) Sulfate mineral(s) Sulfide mineral Sulfur-bearing minerals zeolite group minerals?
clay minerals?
Qz, Cri, Tri Gyp, Anh, Alu Pyr Gyp, Anh
Textural description -no traces of alteration Groundmass: consisting of fine aggregate of anhedral silica minerals, unclear crystal boundary of microlite and tabular to irregular voids
Original volcanic rock textures are replaced to silica minerals and minor hydrothermal clay mineral(s)
[Type 3-2C]
An aggregate of coarse euhedral sulfate crystals
[Type 3-2F]
Euhedral sulfate crystals included in the aggregate of fine silica and clay minerals
Mainly pyrite and sulfate minerals with minor silica and clay minerals Minor but commonly contain gypsum and/or anhydrite crystals