WEATHERING-MEANINNGAND EFFECTS

We are learning today

What is weathering?Different types of weathering.

Effects of weathering.

What is weathering?

Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact

with the Earth's atmosphere, biota and waters. Weathering occurs in situ, or "with no movement",

and thus should not be confused with erosion, which involves the movement of rocks and minerals by

agents such as water, ice, wind, and gravity.

THREE TYPES OF WEATHERING

1.Mechanical weathering or Physical weathering.

2.Chemical weathering.3.Biological weathering.

P hy s i c a l w e a t h e r i n g i s t h e c l a s s o f p r o c e s s e s t h a t c a u s e s t h e d i s i nt e g ra ti o n o f r o c k s w i t h o u t

c h e m i c a l c h a n g e . T h e p r i m a r y p r o c e s s i n p hy s i c a l w e a t h e r i n g i s a b ra s i o n ( t h e p r o c e s s b y w h i c h c l a s t s a n d o t h e r p a r ti c l e s a r e r e d u c e d i n

s i ze ) . H o w e v e r, c h e m i c a l a n d p hy s i c a l w e a t h e r i n g o ft e n g o h a n d i n h a n d . P hy s i c a l w e a t h e r i n g c a n o c c u r d u e t o t e m p e ra t u r e ,

p r e s s u r e , f r o s t e t c . Fo r exa m p l e , c ra c k s ex p l o i t e d b y p hy s i c a l w e a t h e r i n g w i l l i n c r e a s e t h e s u r fa c e a r e a ex p o s e d to c h e m i c a l a c ti o n .

F u r t h e r m o r e , t h e c h e m i c a l a c ti o n o f m i n e ra l s i n c ra c k s c a n a i d t h e d i s i nt e g ra ti o n p r o c e s s .

Mechanical weathering

Diff erent types of mechanical weathering

1. Granular disintegration.2. Exfoliation.3. Frost action.

4. Block disintegration.

Granular disintegrati on

A form of weathering where the grains of a rock become loosened. Grains fall out to leave a pitted, uneven surface. Granular disintegration may be the

result of freeze-thaw, hydro-fracturing, thermal expansion, or salt weathering.

Exfoliati on

Exfoliation is the process in which rocks weather by peeling off in sheets rather

than eroding grain by grain.

Frost acti on

This processes include frost shattering, frost-wedging and freeze-thaw weathering. This type of weathering is common in mountain areas where the temperature is

around the freezing point of water. Certain frost-susceptible soils expand or heave upon freezing as a

result of water migrating via capillary action to grow ice lenses near the freezing front

Block disintegrati on

In daytime, intense solar heating causes rocks to expands. At night, the temperature falls so rocks cool and contrasts. Repeated expansion and contraction

produces stress along joints. Joints are then widened and deepened and finally break down the rocks block

by block.

Chemical weathering.

Chemical weathering changes the composition of rocks, often transforming them when water

interacts with minerals to create various chemical reactions. Chemical weathering is a gradual and ongoing process as the mineralogy of the rock

adjusts to the near surface environment.

Diff erent types of chemical weathering

1. Solution2. Hydration3. Oxidation

4. Carbonation

Soluti on

Salt crystallization may also take place when solutions decompose rocks (for example,

limestone and chalk) to form salt solutions of sodium sulfate or sodium carbonate, of which the moisture evaporates to form their respective salt

crystals

Hydrati on

Mineral hydration is a form of chemical weathering that involves the rigid attachment of H+ and OH-

ions to the atoms and molecules of a mineral.When rock minerals take up water, the increased

volume creates physical stresses within the rock. For example iron oxides are converted to iron hydroxides

and the hydration of anhydrite forms gypsum.

Oxidati on

Oxidation affects the iron minerals found in a large variety of rocks, when iron comes into

contact with oxygen in the presence of water it "rusts" and takes on the familiar red colour

Carbonati on

Carbonation occurs on rocks which contain calcium carbonate, such as limestone and chalk. This takes place when rain combines with carbon

dioxide or an organic acid to form a weak carbonic acid which reacts with calcium carbonate (the

limestone) and forms calcium bicarbonate.

Biological wethering

Living organisms may contribute to mechanical weathering (as well as chemical weathering, see 'biological' weathering below). Lichens and mosses grow on essentially bare rock surfaces and

create a more humid chemical microenvironment. The attachment of these organisms to the rock surface enhances physical as well

as chemical breakdown of the surface microlayer of the rock. On a larger scale, seedlings sprouting in a crevice and plant roots exert

physical pressure as well as providing a pathway for water and chemical infiltration.

Positi ve and negati ve eff ects of weathering?

Weathering might be considered the gradual deterioration of "stuff".

It is part of a natural process of erosion, and deterioration of plant and animal matter as well as minerals which then

becomes nutrients for the next generation of plants.

Unfortunately when these natural cycles hit our homes and items we wish to be "permanent", it can be a big pain with

needing to repaint or otherwise repair weathered paint, and wood. Roofing wears out and leaks or needs replacing. Cars

oxidize, or rust.

Many people do like the looks of weathered wood as it often looks somewhat muted over the pristine freshly cut wood.

I suppose that without weathering and deterioration, that we would be in bad shape. Think of what it would be like if

garbage, litter, and discards would just last forever.

BY SANJAY

SUBHAM