Phase II - soils and tephra sampling geologic research project, Drakesbad Meadow, Lassen Volcanic National Park, California

Advanced Geologic Exploration, Inc.

"Preliminary findings shows the Middle Drakesbad Meadow is a product of a complex interplay between the development of organic-rich soils on a prograding alluvial fan and the formation of mineral soils on an active floodplain where flood scour and fill processes dominate. F~gure7 shows a schematic of this relationship. Soils with organic-rich profiles greater than 10 inches thick are located across the northern half of the Middle Meadow, and the maximum organic-rich profile was 29 inches thick. The soils were predominately peat loams to mucky loams, both of which indicate total organic carbon contents shy of the organic soil or Histosol classification. Although only one horizon from one soil profile met the criteria for Histosols, it is likely many of these organic-rich oils could classify as hydric soils. No soil met the classification of fen. The organic-rich soils are stratified, forming paleosols related to changes in soil forming processes and aggradational conditions. Longitudinal profiles suggest a thickening southward over time and along with the angular-shaped grains, confirms an alluvial fan geomorphic province. The mineral soils are relatively thin packages of soils, usually containing an upper peat-rich horizon that is underlain by a thin mineral soil with less organic matter. These are typical floodplain soils whereby over bank flood waters scour the surface soil, then bury it with thin deposits of fine-grained sediment. The mineral soils are located along the southern half of the meadow closest to Hot Springs Creek. Buried soils are common in both the mineral and organic-rich soils and have been subdivided into four paleosol intervals. Although similar characteristics exist between the mineral and organic-rich paleosols, their relationship is unclear at this time. All the soils show immature soil development and were likely formed since the mid to late Holocene. Charcoal fragments are found in many paleosols and may provide a means of dating the soils and provide insights to their formation. Analysis of the Bathhouse Ash revealed it was not a tephra, but a kaolin day layer associated with Boiling Springs Lake out flows, and thus, is not directly useful for dating purposes. Other white layers discovered in meadow cores are probably not tephras either, and analysis is likely to show they are from either Devils Kitchen or Boiling Springs Lake. Differential settlement between soil cores and a sand-filled fissure found in one soil core appear the result of tectonic processes from large nearby earthquakes."