Breccia/Tuff Green-> Red
|[ Sizes: Orig | Large | Med | Small | Thumb ]|
Many of the rock layers are composed of a breccia of volcanic fragments from earlier parts of the volcano, held together with a matrix of altered ash. The ash is slightly green, reflecting the small divalent iron content. However, when a crack permits hydrothermal oxidation, some of the divalent iron becomes trivalent, and turns from greenish to reddish.