11:30 AM - 11:45 AM
★ [MIS03-06] Pedogenesis of tephra-derived soils in Japan
Keywords:soil, tephra, pedogenesis, tephra-derived soil, Andosols/Andisols, phytolith
Pedogenesis includes both ‘topdown’ and ‘upbuilding’ models (Almond and Tonkin, 1999; Lowe, 2000; Inoue, 2001). Topdown pedogenesis is ‘classical’ soil formation that occurs by leaching, illuviation, and other processes that form andic materials with horizons developing in a downward-moving front. Upbuilding pedogenesis operates where the soil forms while additions to the soil surface of such materials as tephra or loess occur. If additions are sufficiently slow — typically as thin incremental deposits in distal areas — then topdown pedogenesis continues while the land surface slowly rises (referred to as ‘developmental upbuilding’). If additions are thick or frequent, as typically occurs nearer volcanic sources, then the antecedent soil is buried and isolated, and soil formation begins again on the new materials at the land surface (‘retardant upbuilding’) (Inoue et al., 2011b; Lowe et al., 2008). The profile character is thus determined by the interplay between the rate at which tephras are added to the land surface and topdown processes. Understanding Andosol/Andisol genesis thus often requires a stratigraphic approach combined with an appreciation of buried soil horizons and polygenesis (Lowe and Tonkin, 2010). The terms ‘developmental upbuilding’ and ‘retardant upbuilding’ were first used by Johnson and Watson-Stenger (1987) and Johnson et al. (1990) as part of their dynamic-rate model whereby soils evolve by ‘ebb and flow’ through time (Schaetzl and Anderson, 2005). As mentioned above, most of the tephra-derived soils in Japan are formed by upbuilding pedogenesis and may be described as multisequal soils.
At the present day, theories concerning pedogenesis of tephra-derived soils in Japan are changing from long-established theories. The soils in the regions having numerous active volcanoes occur distinctive pedogenesis unlike in non-volcanic regions.