Definitions: Weathering: the break-up of rock at earth’s surface Erosion: the physical removal and transport of rock material by water, wind or ice. Mass wasting: the movement of large amounts of rock or soil downslope due to gravity (landslide)

Weathering Earth’s surface is constantly changing. It is a dynamic (changing) planet. 200 years ago most people believed that mountains, lakes and deserts were permanent (static) features of the Earth.

Earth’s surface is continually being sculpted by… Name 5 forces…. Water Wind Ice (glaciers) Plate Tectonics (Volcanoes/Earthquakes) Biological (humans)

Weathering processes are part of the rock cycle.

Weathering is an External process Processes that occur on the Earth’s surface (wind, water, ice) get their energy from the Sun.

Internal processes These processes that change the earth’s surface, get their energy from magma within the Earth (mantle) Plate tectonics change shape, size and location of land masses. Volcanic activity Mountain building Earthquakes

Mechanical (physical) weathering (Def.) The physical break-up and the chemical decomposing of rock due to exposure and processes at or near the Earth’s surface. It’s a s-l-o-w and subtle process. All materials are susceptible to weathering Two types of weathering: Mechanical (physical) weathering Chemical weathering

Mechanical (physical) weathering The disintegration, fragmenting, splitting, breaking of rock into smaller and smaller pieces. The rock’s mineral composition remains unchanged.

Mechanical weathering involves several physical processes: 1. Frost wedging 2. Abrasion 3. Exfoliation 4. Biological activity

Frost wedging Repeated freezing and thawing. Water expands about 9% in volume when it freezes. Expanding exerts tremendous outward force. Water works it way into cracks and pores in rocks, breaking them into pieces when it freezes-thaws.

Frost wedging

Weathered rock piles-up at the base of a cliff forming a TALUS slope

Talus (weathered rock rubble) at the base of a slope

Frost-wedging occurs in mid-latitudes (that’s us) and mountainous regions where daily freeze-thaw weather exists. (not Florida) Frost wedging is responsible for pot holes and road repairs.

Abrasion: Due to … Water Wind Glaciers The scraping and wearing down of rocks. Due to … Water Wind Glaciers

Abrasion by water: Rocks tumble and collide as they are carried by rivers and streams

Abrasion by waves crashing onto rock break it down over time

Abrasion due to wind carrying sand (quartz) eroding rock

Sand-blasting graffiti off a brick wall using water, silica sand (quartz) and air pressure is an example of abrasion.

Abrasion due to glaciers: ice and rock fragments slide over bedrock scraping, scratching, polishing rock as it moves

Exfoliation (uploading) As sedimentary rock erodes away, Igneous rock (granite) is uplifted and exposed. With LESS PRESSURE (weight) on it, The granite breaks loose in layers (like an onion).

Uplift and exfoliation What rock is this?

More exfoliated rock from Stone Mountain, Georgia Ahhhh, I can finally relax, and expand with all that pressure off of me!

Biological Weathering Plant roots grow into fractures and wedge the rocks apart as they grow.

Biological weathering Mosses and lichens grow on rocks, slowly breaking them down over time.

Animals and insects burrow into soil thus exposing the bedrock to the elements

Human activity such as mining and construction blasting weathers rock.

Bell work ??????? What 4 ways does rock mechanically weather? F______________ a. scraping, sand A______________ b. plants, animals E______________ c. freeze, expand B _____________ d. peeling, pressure Rost-wedging c. Brasion a. Xfoliation d. Iological b.

Chemical Weathering Rock is Decomposed (chemically changed) by agents such as WATER: (hydrolysis) dissolves minerals in some rocks into ions.

Chemical weathering by water Acids: weak carbonic acid formed when (CO2 + rainwater = acid rain) dissolves minerals, calcite (limestone and marble). Sulfur dioxide an nitrogen compounds released from industries, produce acid rain that weathers structures made of concrete, stone and metal.

Which is made of granite and which is made of marble Which is made of granite and which is made of marble? Which has been chemically weathered?

Oxygen: combines with metals to form oxides (such as iron oxide Fe2O3 or rust). This is called oxidation.

Caves and caverns are formed by dissolved minerals precipitating out of solution.

Factors that affect the Rate of Weathering Not all rocks weather the same! Name 4: The minerals that compose the rock. (hard vs. soft minerals) 2. How much surface area is exposed. (small pieces weather faster) 3. The climate that the rock is in. ( temperature and precipitation) 4. TIME! (more time – better)

Factor 1. Composition and Hardness weathering rate Minerals that weather easily. Feldspar (breaks down into clay minerals – a major component in soils and shale) olivine Mica Calcite Gypsum Marble rock Minerals that resist weathering Quartz (7 on Mohs hardness scale) (ends up as sand on beaches)

Factor 2. Exposed surface area and weathering rate. Rock that is broken into smaller pieces has more surface area that is exposed to weathering.

Factor 3. Climate and weathering rate. Dry, cold climates = s-l-o-w weathering Warm, humid, wet climate = rapid weathering

Bellwork Abrasion a. physical (mechanical) Rusting weathering Exfoliation Frost-wedging b. chemical weathering Fizzing

Graph 1 Weathering of rock Time

Graph 2 * granite? * halite? Mass of rock Chips marble Time

Graph 3 Rounding of rocks Time in Water

Chemical Weathering (acid) Graph 4 Amount of Quartz in the Rock Calcite Chemical Weathering (acid) Quartz

Graph Part 1 Amount of Exposed Surface Area Amount of Weathering

Graph Part 2 Hardness (Mohs) 1 talc 3 halite 10 diamond 7 quartz Degree of Abrasion

Amount of Chemical Weathering (acid) Graph Part 3 Amount of Calcite in the Rock Amount of Chemical Weathering (acid)

Graph Part 4 Fe Concentration Amount of Oxidation

Graph 5 Soil Production Weathering of Rock