Weathering Flashcards
(24 cards)
What are examples of physical weathering?
freeze/thaw (frost wedging), stress release (exfoliation), isolation (thermal expansion/contraction), abrasion, salt crystalization
What is frost wedging/freeze-thaw?
When water fills the crack. Expands when freezes, so that will break the rock. Like what happens to sidewalks. It’s the swings in temperatures that allows this to happen. Ice freezes, will seep into cracks, then as it gets colder will pluck. Seen in mountainous areas. Also what happened to old man of the mountain in NH.
What is exfoliation?
When there is a pluton, the weight from the surface will push down, keeping it confined. As weathering happens at the surface and the pluton gets exposed, there isn’t confining pressure and the pluton will expand and flake. The expanson cracks the top layers like an onion.
What is abrasion?
Two objects knocking into each other. This happens in rivers when they carry along sediment and rocks which hit other rocks, breaking them down. Wind can also do it by carrying sand and smoothing down a surface (like sandpaper).
What is salt crystallization?
Salt crystallization weathering, also known as haloclasty, is a type of physical weathering where the growth and expansion of salt crystals within rocks and concrete exerts pressure, causing them to break apart
What is spheroidal weathering?
Weathering at the joints. A process in which solid rock masses cut by intersection roughly cubical joint pattern weather into spherodial cores.
What are some ways of chemical weathering?
Dissolution, carbonation, hydrolysis, oxidation
What is carbonation?
Carbonation is the process of rock minerals reacting with carbonic acid. Carbonic acid is formed when water combines with carbon dioxide. Carbonic acid dissolves or breaks down minerals in the rock.
CO2 + H2O → H2CO3
(carbon dioxide + water → carbonic acid)
CaCO3 + H2CO3 → Ca2+ + 2HCO3-
(calcite + carbonic acid → calcium + bicarbonate)
What is hydrolysis?
The replacement of cations in a mineral structure by hydrogen ions derived either from water or more likely acid. Releases to the solution the cations replaced in the mineral structure by H and either converts the original mineral into a different minerals or dissolves it completely. H ion + Mineral with mobile cations = entirely dissolved mineral or partially altered mineral in which H ions replace mobile ions that are put into solution.
What is oxidation/reduction weathering?
Atmospheric oxygen gains electrons and is reduced as mineral constituents lose electrons and are oxidized, producing new “rusted” minerals.
Most obvious example is with iron, ferrous iron turned into reddish-orange ferric iron.
Pyroxene plus atmospheric oxygen and water will turn into limonite and dissolved silica.
Study this weathering table
study this mineral weatherability table
If the average igneous rock is weathered by mechanical weathering, what do you typically get? Chemical? Solution? How would this help you?
Sand
Clay
Dissolved salts
The quartz-feldspar ratio could tell you if it was a wet or dry climate. You don’t get soil in dry climates.
Study this chart about weathering
What are the different horizons in soil and what are they called?
The top is O horizon (for ogranic, humus), second down is A horizon (zone of leaching), then B horizon (zone of accumulation), then C horizon (partially decomposed parent material)
What is the A horizon in soil
Consists of humus mixed with sediment. Part of the top-soil.
What is the B horizon
Accumulation. Absent in young soils. Distinct in old soils. Al, Fe, Clay (moist environments). Si, Ca in arid climates
What is the C horizon?
parent material, incompletely weathered parent material
What is simple solution (dissolution)?
The chemical reaction of solid rocks and minerals with water or acid. Cones between ions in rigid crystalline lattices are broken and the freed ions are disseminated in solution. Like limestone with acid. Rain has a small amount of carbonic acid, so it weathers limestone. Also halite in water.
What do soils consist of?
Weathered bedrock material that produces much of the sediment, the organic material added by living organisms, and add’l chemical elements that move through the soil in groundwater.
What is the zone of leaching?
Near the surface, where the water dissolves ions and carries away the fine clays moving down into the zone of accumulation.
What happens in the zone of accumulation in soil?
Here the ions precipitate as new minerals and the clays settle out.
What is humus as it relates to soil?
Found in the O horizon, it is partially decayed organic matter.
What is insolation weathering?
Insolation weathering, also known as thermal stress weathering, is a type of physical weathering caused by the expansion and contraction of rocks due to temperature fluctuations, leading to cracks and eventual breakdown
