weathering erosion interactive[1]

8/2/2019 Weathering Erosion Interactive[1]

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Weathering
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What is weathering?

Weathering is a set of physical, chemical

and biological processes that change

the physical and chemical properties ofrocks and soil at or near the earth's

surface.
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What is weathering

Weathering is the response of materials which were in

equilibrium within the lithosphere to conditions at or near

its contact with the atmosphere, the hydrosphere, and

perhaps still more importantly, the biosphere.

Reiche, 1950

Weathering is the breakdown and alteration of minerals

near the earths surface to products that are more in

equilibrium with the newly imposed conditions.

Olllier, 1984
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More about weathering

Definition the breakdown of rock to form

sediment [very small pieces of rock]

Weathering happens to rocks that are NOT

MOVING

Weathering is part of the Rock Cycle
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Types of weathering

Mechanical (physical]

Chemical Biological
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Mechanical weathering breaks rocks down into smaller pieces.
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Types of mechanical weathering include

frost wedging,

exfoliation and

thermal expansion.
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Enchanted rock is a

huge example of

exfoliation

mechanical

weathering
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Chemical weathering breaks rocks downchemically adding or removing chemical

elements, and changes them into other

materials.

Chemical weathering consists of chemical

reactions, most of which involve water.
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Precipitation

Evaporation


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In chemical weathering, a rock is

broken down by chemical reactions

that change its mineral composition

and physical and chemical properties
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Chemical weathering happens when the

minerals that make up a rock are

changed, leading to the disintegration of

the rock


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Chemical weathering happens quickly in

warm, moist environments because water is

needed for the chemical reactions.

The warm weather speeds up the reactions.


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Not all minerals are prone to chemical weathering.

For example, feldspar and quartz, are common minerals in therock granite, have very different levels of resistance to

chemical weathering.Quartz doesnt weather very easily, but feldspar does. Over along time, it chemically changes into clay minerals.

Highly weatherable Olivine

Augite

Hornblende

Biotite

K-feldspar

Muscovite

Highly resistant Quartz

In

creasingsta

bility
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Chemical composition water is ideally controlled by

Climate and hydrologic conditions

Rock - water interaction

Anthropogenic inputs

Direct addition of salts
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Two types of weathering mechanisms control water composition :

Congruent weathering mechanism :

No solid by - product is formed

CaCO3 + H2O + CO2 = Ca2+ + 2HCO3-

Incongruent weathering mechanism :

Solid by - product is formed

Feldspar + CO2 + H2O = Kaolinite + Cation + SiO2 + HCO3

Rock - Water Interaction
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Chemical Processes

Dissolution Hydration

Hydrolysis Direct attack by acidsChemical precipitation Base exchange

Reduction of sulfate Concentration

UltrafiltrationOxidation - reduction reactions


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DissolutionDissolution is first step in chemical evolution of water. It affects both

gases and solids. Typical regions of gas dissolution by groundwater are :

Soil zone

Vadose zone / unsaturated zone

Zones of oil and gas accumulations

The gases commonly interacting with groundwater include N2, Ar, O2,

H2, He, CO2, NH3, CH4 and H2S.

Dissolution of gases may render the water acidic means chemically

aggressive. Degree of dissolution depends on the solubility of the

minerals, the antecedent concentration of water and the pressure and

temperature of the locality.
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Soluble rocks include limestones, dolomites,

halites, gypsum etc.

Silicates are relatively insoluble rocks.
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Hydration

Hydration is the penetration of water into thecrystal lattice of minerals or attachment of water

molecules to the ions of dissolved salts. It is first

step in weathering of minerals e.g.

anhydrite ------- to --------- gypsum

biotite -------to --------- vermiculite


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Hydrolysis

Hydrolysis is reaction of any substance with water. Hydrolysis is the

reaction of an ion with water to form an associated species plus H+

orOH-.

Hydrolysis of cations produces slightly acidic solution as per equation

M+ + H2OMOH + H+

Anion hydrolysis results in basic solution as per equation

X- + H2O HX + OH-

The process is effective only if :

Produced ions are removed from solution

Required ions are added to the solution

At equilibrium cessation of dissolution occurs
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Oxidation - Reduction Reactions

These are chemical reactions in which electrons are transferred from one

atom to another. In oxidation there is loss of free electrons by the substancebeing oxidized and in reduction there is gain of electrons.

Oxidation as a process of modifying water quality is important in vadose

zone due to supply of O2

from air and from CO2.

Oxidation processes include

oxidation of sulphides, producing Fe2O3, H2SO4 and CO2 with acids attacking

carbonates, magnetite, producing limonite; and organic matter such as lignite,

coal and bitumen producing CO2.

Reduction is important in organic deposits constituting reducing chemicalenvironments. In these cases oxygen may be applied from oxides, sulphates,

nitrates as well as nitrites and from various gases.

Ch i l P i it ti
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Chemical Precipitation

Precipitation of dissolved mineral matter occurs due to reasons :

Reaction with ions from the solid framework to form insolubleprecipitates e.g. formation of CaF2 due to reaction of F in water

with Ca from country rock.

Changes in temperature and pressure affecting solubility of ions

as in precipitation of tufa around spring orifice on CO2 release.

Oxidation of dissolved matter exposed to air resulting in

components of decreased solubility such as precipitation of ferric

hydroxide (Fe(OH)3) from waters containing ferrous iron

(Fe(OH) 2) in solution.
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Base Exchange

Ion exchange is the process in which ions and molecules adsorbed on

surfaces of solid substances by physical and chemical forces (van der

waals attraction and chemisorption respectively) are exchanges forions in the water.

Substances capable of ion exchange are

clay minerals,

zeolites, ferric oxide and

organic matter

because they form colloids of large surface areas. e.g. replacement

of Ca by Na or Mg in bentonite resulting into natural softening of

water by enrichment in Na and increased porosity and permeabilityof the newly formed Ca- and or Mg- based clay mineral.
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Reduction of sulfate

It is due to bacteria and contact with organic matter (coal,

lignite, petroleum) and results in the removal of sulfates

from the transporting groundwater.

One example of reaction of sulfate water in contact with

methane :

CaSO4 + CH4 CaS + CO2 + 2H2O

CaS + 2CO2 + 2H2O H2S + Ca(HCO3)2
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Concentration

Concentration of TDS content in groundwater may be affected by :

Evaporation of water

Solution of mineral matter

Chemical reactions

Concentration by evaporation is operative in the soil moisture zone and

between rainfall events. The process can lead to soil / water salinisation

and formation of continental salt deposits.

Concentration by solution is on account of soluble minerals in the

subsurface..
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Structural breakdown of silicate minerals in the basalt

(Equations 2 to 4) is accompanied by : release of Ca + Mg predominantly from weathering of

olivine + augite with

lesser contribution of Na + Ca from the plagioclasefeldspar,

which is subsequently affected by post dissolution

geochemical changes such as cation exchange by zeolitesand precipitation of CaCO3 .

Summary
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How are erosion & weathering different?

Weathering involves two processes (mechanical,

chemical)that often work together to break down

rocks. Both processes occur in place. No

movement is involved in weathering.


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As soon as a rock particle (loosened by one of the two weathering

processes) moves, we call it erosion or mass wasting.

Mass wasting is simply movement down slope due to gravity.

Rock falls, slumps, and debris flows are all examples of mass wasting.

We call it erosion if the rock particle is moved by some flowing

agent such as air, water or ice.


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In a nutshell: if a particle is loosened,

chemically or mechanically, but stays put,

we call it weathering.

Once the particle starts moving, we call iterosion.


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Painted Desert National Monument : Wind erosion
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Biological weathering is the breakdown of rock

caused by the action of living organisms,

including plants, burrowing animals, and lichens.

A lichen is a combination of fungus and algae, living

together in a symbiotic relationship.Lichens can live on bare rock, and they break down rocks

by secreting acids and other chemicals.


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Biological weathering involves processes that can

be either chemical or physical in nature.

Biological weathering can be considered special

types of mechanical or chemical weathering.


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Biological weathering What is it?


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Some biological weathering processes are:

1. Rocks can break because of animal

burrowing.

2. Tree roots grow into cracks and widen them,which helps physical weathering.

3. Bacteria, lichens and other organisms

secrete acidic solutions, which helps chemicalweathering.


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Lichens on rocks cause biological weathering.


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Plants growing in rocks break the rocksapart.


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What is erosion?

Erosion is defined as the removal and

movement of earth materials by natural

agents.Some of these agents include glaciers,

wind, water, earthquakes, volcanoes,

tornadoes, hurricanes, mud flows, andavalanches.

Wh h diff f


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What are the different types oferosion?
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Water is the most importanterosional agent and erodes

most often as running water instreams or rivers.


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Water in all its forms is erosional. Raindrops

create splash erosion that moves tinyparticles of soil. Water collecting on thesurface of the soil collects as it movestowards tiny streams and creates sheet

erosion.


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Erosion by wind is known as aeolianerosion (named after Aeolus, the Greek

god of winds) and usually occurs in

deserts.

Aeolian erosion of sand in the desert is

partially responsible for the formation ofsand dunes.


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The erosive power of moving ice isactually a greater than the power ofwater.

However since water is much morecommon, it is responsible for a greateramount of erosion on the earth's surface.


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Glaciers cause erosion two ways - they pluck

and abrade. Plucking takes place by waterentering cracks under the glacier, freezing,

and breaking off pieces of rock that are thenmoved by the glacier. Abrasion cuts into the

rock under the glacier, scooping rock up like

a bulldozer and smoothing and polishing the

rock surface.
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Athabasca Glacier - Jasper, Canada


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Waves in oceans and other large bodiesof water cause coastal erosion.

The power of ocean waves is awesome;

large storm waves can produce 2000

pounds of pressure per square foot.The pure energy of waves along withthe chemical content of the water is

what erodes the rock of the coastline.
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Wave action in Calvert County Maryland

weathering erosion interactive[1]

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