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HAWAII
A tropical soil!
Hematite and clay-rich soils are very common in Oahu. The combination of an old landscape (this one lies on the Waianae shield volcano: 3.8-2.95 Ma) under tropical conditions, favoured the formation of strongly weathered soils, mostly Ultisols or Oxisols.
Basalt saprolite
A basalt saprolite with spheroidal weathering patterns. Very soft material on the edges with a harder core.
Spheroidal basalt weathering
A classic example of spheroidal weathering of basalt, with the typical "onion-like" appearance.
A baked zone or pre weathered material?
Multiple lava flows and a red layer in between. This red layer has around 10 cm and expands horizontally. Could this be the effect of the thermal alteration by the overlying basalt deposition or signs of initial weathering stages that were buried by the new deposition?
Volcanic tuff hit by a basalt!
This basalt fragment felt on the unconsolidated tuff (yellowish matrix). The shock patterns are still visible.
Volcanic tuff
Another beautiful display of weathered volcanic tuffs on slopes facing Hanauma Bay. Small and medium-sized basalt fragments are widespread on the tuff.
Surface of a Vertisol
Cracked surface of a Vertisol, which is a soil order rich in expansive clays, like smectites. Upon drying, they tend to shrink, when wet, they swell.
This soil order occurs in some footslopes and toeslopes on Oahu Island, where solute transport from upslope, rich in Silica and other cations, provides the ingredients for clay neoformation.
This soil order occurs in some footslopes and toeslopes on Oahu Island, where solute transport from upslope, rich in Silica and other cations, provides the ingredients for clay neoformation.
Expansive clays in action!
Another classic example of how expansive clays behave upon drying.
Expansive clays
A closer look at the fragments formed on the surface after drying and shrinking clays. These are heavy and hard blocks, which become very plastic and sticky when wet. These are complicated soils for management due to their physical properties.
A ravine on the make
A collapse of part of the slope formed by volcanic tuff. The whole landscape is highly susceptible to erosion as can be seen by numerous soil exposures and small ravines. It provides a nice view of the layered structure of the pyroclasts deposition.
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