Weathering

Weathering Weathering Landscapes Weathering vs. Erosion Joints: Setting the Stage Physical (Mechanical) Weathering Chemical Weathering Products and Forms Made by Weathering Weathering Landscapes

6. Weathering Landscapes Consider a common rock – granitic rocks (granite, granodiorite, tonalite, diorite …) made up of interlocking minerals

Decay of weak minerals (biotite, feldspar) separates grains and makes granite sand called - GRUS

Grus produced most rapidly where joints intersect

Granular distintegration – seen on rock surfaces

rounds edges of petroglyphs – blurring petroglyphs

Crumbly distintegration – grains weathered to powder

Grus erosion from joints creates rounded forms at Mt Rushmore

Core stones made when corners of granite blocks weathered into grus

Core stones in subsurface are “emerge” onto the surface as the grus washes away with rain and flowing water, because they are too big to be carried by water

Grus washes away easily with rain, leaving piles of core stones - tors

Tors (piled up core stones) very common in the Sonoran Desert

Granite weathering took a long time in the subsurface (from groundwater) – spheroidal forms were then exposed by erosion of grus

Erosion of weathered material by flaking (fingernail thick)

Erosion of weathered material by Scaling – thicker

Rock Art Panels Host Dozens of Weathering Forms How many can you identify?

Rock Art Panels Host Dozens of Weathering Forms How many can you identify?

Encourage Site Stewardship to Protect Priceless Cultural Heritage

Imagery seen in this presentation is courtesy of ASU faculty, Paradise Valley and Mesa CC faculty, students and colleagues in other academic units, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city, state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.