Early Stage Transformation of 2 : 1 Layer Silicates in Pyroclastic Deposits from the 1980 Eruption of Mt. St. Helens
スポンサーリンク
概要
- 論文の詳細を見る
Chemical weathering and pedogenesis are especially rapid in volcanic materials due to their glassy nature, fine particle size, and high porosity and permeability. Early stage mineralogical transformations (0-10 yr) in pyroclastic deposits from the 1980 eruptions of Mt. St. Helens were examined in a cryic-udic climatic regime of western Washington. Chemical weathering in pyroclastic flow deposits near the volcano was strongly affected by acidic precipitation (pH=3.6 to 5.2) originating from sulfuric acid emanating from the vent and by the microtopography that displayed an undulating surface with about 30 cm of relief. Weathering was more intense in depressions because they collected more water than adjacent mounds. Detrital 2 : 1 layer silicate minerals present in the original deposits of the depressions were degraded within five years to poorly crystalline kaolin and noncrystalline hydroxy-Al polymers and aluminosilicates. In the mound landscape position, there was no apparent alteration of the detrital 2 : 1 layer silicates. In forested areas receiving airfall tephra, weathering reactions were driven by carbonic acid originating from CO_2 diffusion from the buried soil. Aluminum released by weathering was preferentially retained as Al-humus complexes and hydroxy-Al interlayers of 2 : 1 layer silicates, which inhibited early formation of allophanic materials. We conclude that 2 : 1 layer silicates in pyroclastic deposits can be rapidly transformed with the resulting weathering products controlled by the dominant proton donor.allophanenoncrystalline materialspedogenesissmectitevolcanic ashvolcanic soilsweathering
- 東北大学の論文