Weathering Forms

Weathering 1. Weathering Products 2. Weathering Landscapes

1. Weathering Products Quartz Sand: quartz is one of the last minerals to decay – it survives weathering & erosion to be deposited in

Rock Coatings

Nutrients - released from mineral weathering Calcium Sodium Magnesium Potassium

Clay Minerals Formed

Clays represent Earth’s ultimate decay of rock

If have too much clay, it shrinks & swells

2. Weathering landscapes Transport-limited landscapes: where the rate of transport (detachment and erosion) is smaller than the rate of weathering. Weathering > Transport Weathering landscapes: where Transport > Weathering

The balance between weathering and erosion defines the landscape

In deserts – transport is faster

You see bedrock, because weathering particles eroded away

Humans can upset the balance and accelerate erosion. So when transport (detachment and erosion) becomes faster than weathering, landscapes are not sustainable.

Granitic 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

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

Tors often take on significance to people

Used core stones in Portugal

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

Dome forms produced the same way: subsurface weathering in joints Granite that is not heavily joined becomes domes after grus washed away Rio de Janeiro - Sugar Loaf

Half dome was made in the subsurface in tropical times and exposed by erosion of grus

Karst Topography: entire landscape made by dissolution weathering

Other rocks can also dissolve to form karst (gypsum, rock salt)

If exposed see grooves (karren)

Solution doline – dissolve fastest in joints

“Sinkhole” (doline)

Can also create doline by collapse

Florida – lots of groundwater pumping & roof of cave collapses Before Development After solution doline

Sinkholes merge to form Uvale valley

“Blind” rivers flow down sinkholes into cavern systems

Caves Formation Limestone Cave

Caves Features

Stalagtite Stalagmite Speleothems: Cave formations

Limestone Caves Step 1: Groundwater dissolves limestone, most aggressively at the water table. Also, groundwater follows lines of weakness in the limestone enlarging caves. Step 2. When the water table drops, stalactites and stalagmites can form on the roof and floor, respectively.

The water table usually drops when the stream has “cut down” to a lower level

Stalagmite – requires lots of time with water table much lower

The southeast China karst region has “tower karst” forms