WEATHERING, EROSION AND DEPOSITION (EXOGENIC PROCESS) / EARTH AND LIFE SCIENCE / SCIENCE 11 - MELC 5

Summary

This educational video delves into exogenic processes, focusing on weathering, erosion, and deposition. It explains how rocks break down through mechanical and chemical weathering, influenced by factors like climate and rock type. The script then describes erosion as the transportation of rock particles by agents like water, wind, glaciers, and gravity, leading to deposition in lower areas. The lesson concludes with sediments transforming into rocks through compaction and cementation, highlighting the geological journey from weathering to rock formation.

Takeaways

• 📚 The video discusses exogenic processes, focusing on weathering, erosion, and deposition as part of the Earth's geological processes.
• 🔨 Weathering is the process where rocks are broken into smaller fragments either chemically or physically due to exposure to various environmental factors.
• 🧊 Mechanical weathering includes processes like frost wedging, exfoliation, and the growth of plant roots in rock cracks, which physically break down rocks without altering their chemical composition.
• 🌡 Chemical weathering involves chemical reactions between rock minerals and substances in the environment, leading to dissolution, oxidation, and hydrolysis.
• 💧 Dissolution is a type of chemical weathering where water molecules break atomic bonds in minerals, pulling ions apart and surrounding them in hydration spheres, keeping them dissolved.
• 🔄 Oxidation in weathering results in new oxide minerals forming on the rock surface, often seen as colored stains due to different ions reacting with oxygen.
• 🌾 Hydrolysis is a chemical weathering process where water interacts with minerals containing aluminum, oxygen, and silicon, forming new clay minerals.
• ⏳ The rate of weathering is influenced by factors such as climate, rock type, rock structure, slope, and duration of exposure.
• 🌊 Erosion is the movement of rock particles from one place to another by agents like water, wind, glaciers, and gravity, which carry the particles until they lose energy and are deposited.
• 🏔 Deposition occurs when eroded rock sediments are dropped off by agents of erosion, usually in lower elevation areas, forming sediment piles with distinct characteristics.
• 🗻 Over time, these sediment piles can turn into rocks through processes of compaction, where clay particles stick together, or cementation, where minerals crystallize and bind the grains together.

Q & A

What are the three main exogenic processes discussed in the video?

The three main exogenic processes discussed in the video are weathering, erosion, and deposition.

How does weathering break rocks into smaller fragments?

Weathering breaks rocks into smaller fragments either chemically or physically due to exposure to varying temperature, pressure, substances, and biological actions.

What are the two types of weathering mentioned in the script?

The two types of weathering mentioned are mechanical weathering, which involves physical breakdown without chemical alteration, and chemical weathering, which requires a chemical reaction between rock minerals and environmental substances.

Can you explain the process of frost wedging in mechanical weathering?

Frost wedging occurs when water fills cracks in a rock and freezes overnight. As ice expands, it wedges the cracks open further, breaking off pieces of rock that fall and collect at the base of the cliff, creating a tailless slope.

What is exfoliation and how does it relate to mechanical weathering?

Exfoliation is a process where a rock, unburdened by overlying rocks, sheds layers due to a reduction in pressure or from the continual expansion and contraction caused by temperature changes. This is a form of mechanical weathering that can occur when rocks are heated and cooled, weakening the outer layers.

How does chemical weathering involve the interaction between rock minerals and the environment?

Chemical weathering involves chemical reactions between rock minerals and substances in the environment, such as dissolution, oxidation, and hydrolysis, which break down the rock into smaller particles or alter its composition.

What is dissolution and how does it contribute to chemical weathering?

Dissolution is a chemical process where water molecules break the atomic bonds in minerals or shells, pulling apart ions and surrounding them with hydration spheres. This keeps the ions separated and dissolved in water, contributing to the breakdown of rocks.

How does the acidity of water affect chemical weathering?

Acidic waters, such as those rich in carbonic acid, can speed up chemical weathering by increasing the rate of chemical reactions and the dissolution of minerals.

What factors can influence the rate of weathering?

Factors that influence the rate of weathering include climate, rock type, rock structure, slope, and duration of exposure.

What are the agents of erosion mentioned in the script?

The agents of erosion mentioned are water, wind, glaciers, and gravity, each capable of moving rock particles from one place to another.

How does deposition occur after the process of erosion?

Deposition occurs when the agents of erosion lose energy and can no longer carry the rock particles, leading to the sediments being dropped off at locations usually of lower elevation.

What characteristics of sediment piles can be used to interpret their travel history and maturity?

The characteristics of sediment piles, such as grain compositions, sizes, shapes, and sorting, can be used to interpret their travel history and maturity, indicating the processes they have undergone and their origin.

How does sediment turn into rock through geological processes?

Sediment turns into rock through compaction, where mud-sized grains are squeezed together and water is released, or through cementation, where dissolved ions form crystals that cement the grains together.

Outlines

00:00

🌱 Geological Processes: Weathering, Erosion, and Deposition

This paragraph introduces the exogenic geological processes of weathering, erosion, and deposition. Weathering is the process where rocks are broken down into smaller fragments through physical or chemical means due to exposure to temperature changes, pressure, substances, and biological actions. Mechanical weathering includes frost wedging, exfoliation, and root growth, while chemical weathering involves reactions such as dissolution, oxidation, and hydrolysis. The paragraph also explains how these processes are interconnected and how they contribute to the formation of various geological features.

05:01

🔍 Weathering in Depth: Mechanical and Chemical Breakdown

This section delves deeper into the specifics of weathering, highlighting the mechanisms of mechanical and chemical weathering. Mechanical weathering is further explained through examples like frost wedging, exfoliation, and the role of plant roots and marine organisms. Chemical weathering is discussed in terms of dissolution, where water molecules break atomic bonds, and precipitation, the reverse process. Oxidation and hydrolysis are also covered, with examples of how they affect the appearance and composition of rocks. The influence of environmental factors such as water, temperature, and acidity on the rate of weathering is also discussed.

10:01

🏞️ Erosion and Deposition: The Movement of Rock Particles

The final paragraph focuses on erosion and deposition, describing how weathered rock particles are transported and eventually settle in new locations. Erosion is driven by agents such as water, wind, glaciers, and gravity, each with its unique method of moving sediment. Deposition occurs when these agents lose energy and can no longer carry the sediment, leading to the formation of various sedimentary structures. The paragraph also discusses how the characteristics of sediment, such as grain size and composition, can reveal information about their origin and the processes they've undergone. The transformation of sediment into rock through compaction and cementation concludes the lesson.

Keywords

💡Exogenic processes

Exogenic processes refer to the geological processes that occur at the Earth's surface, primarily involving weathering, erosion, and deposition. These processes are crucial in shaping the landscape and are the focus of the video's discussion. The script explains how rocks are broken down and transported, illustrating the interconnected nature of these processes.

💡Weathering

Weathering is defined as the process by which rocks are broken down into smaller fragments either chemically or physically. It is a key concept in the video, as it sets the stage for erosion and deposition. The script describes two types of weathering: mechanical, which involves physical breakdown without chemical alteration, and chemical, which involves a chemical reaction that changes the rock's composition.

💡Erosion

Erosion is the process of moving rock particles from one place to another. It is a central theme in the video, as it discusses how weathered materials are transported. The script mentions various agents of erosion, including water, wind, glaciers, and gravity, each playing a role in the movement of sediments.

💡Deposition

Deposition is the process where eroded rock particles are dropped in a new location, typically at lower elevations. It is the final stage of the cycle discussed in the video, following weathering and erosion. The script explains how deposition occurs when the energy of the erosional agents is no longer sufficient to carry the sediments.

💡Frost wedging

Frost wedging is a specific type of mechanical weathering mentioned in the script. It occurs when water fills cracks in rocks and freezes, expanding and causing the cracks to deepen. This process is an example of how temperature changes can lead to the breakdown of rocks and is part of the broader discussion on mechanical weathering.

💡Exfoliation

Exfoliation is another form of mechanical weathering described in the script. It happens when rocks, no longer under pressure from overlying rocks, expand and contract due to temperature changes, leading to the shedding of outer layers. This process contributes to the physical breakdown of rocks and is an example of how environmental factors influence weathering.

💡Chemical weathering

Chemical weathering involves chemical reactions between rock minerals and substances in the environment, leading to the breakdown of rocks. The script outlines three major types of chemical reactions: dissolution, oxidation, and hydrolysis. This concept is integral to understanding how rocks are altered at a molecular level.

💡Dissolution

Dissolution is a chemical weathering process where water molecules break the atomic bonds in minerals, causing them to dissolve. The script explains how polar water molecules can separate ions and keep them dissolved as long as there is sufficient water. This process is an example of how chemical weathering can change the composition of rocks.

💡Precipitation

Precipitation, in the context of the script, refers to the opposite of dissolution, where dissolved ions come together to form solid crystals that settle out of water. This process can occur when water evaporates, allowing ions to recombine. It is mentioned in the script as part of the discussion on how dissolved ions can be transported and later deposited.

💡Oxidation

Oxidation is a chemical weathering process where oxygen reacts with dissolved ions to form new oxide minerals. The script uses iron oxide, or rust, as an example of this process, which can leave stains on rock surfaces. Oxidation is a key factor in the alteration of rock composition and contributes to the visual changes observed in weathered rocks.

💡Hydration spheres

Hydration spheres are mentioned in the context of dissolution, where water molecules surround dissolved ions, keeping them separated. This concept is important for understanding how ions remain in solution and do not recombine to form solid minerals. The script uses this term to illustrate the molecular interactions during the dissolution process.

💡Clay minerals

Clay minerals, such as kaolinite, are formed during the process of hydrolysis, a type of chemical weathering. The script describes how these minerals are often white and appear like a fine powder, resulting from the interaction between water and certain minerals containing aluminum, oxygen, and silicon. Clay minerals are an example of the new materials that can form during chemical weathering.

💡Mature sediment

Mature sediment refers to sediment that has been through extensive weathering and erosion processes, resulting in a composition primarily of the most resistant materials, such as quartz and clay. The script explains that mature sediment piles have a distinct character and can be used to interpret the travel history and maturity of the sediment, indicating the extent of the geological processes they have undergone.

💡Compaction

Compaction is the process by which sediments are squeezed together, causing water to be released and the particles to stick together. The script mentions this as one of the ways sediments can turn into rock. It is an essential concept in understanding the transformation of loose sediment into solid rock formations.

💡Cementation

Cementation is the process where dissolved ions from groundwater crystallize and cement sediment grains together. The script describes this as another way sediments can become rock, with examples of common cements including hematite, calcite, and quartz. Cementation is a key concept in the discussion of sedimentary rock formation.

Highlights

The video focuses on exogenic processes including weathering, erosion, and deposition.

Weathering breaks rocks into smaller fragments through mechanical or chemical processes.

Mechanical weathering occurs without altering the chemical composition of rocks.

Frost wedging is a type of mechanical weathering where ice expands in rock cracks.

Exfoliation involves rocks shedding layers due to pressure reduction or thermal expansion and contraction.

Chemical weathering requires a chemical reaction between rock minerals and environmental substances.

Dissolution is a chemical reaction where water molecules break atomic bonds in minerals.

Precipitation is the reverse of dissolution, where dissolved ions form solid crystals.

Oxidation creates new oxide minerals, often seen as colored stains on rock surfaces.

Hydrated ions from dissolution can be transported away by flowing water, leading to precipitation in new environments.

Hydrolysis forms new clay minerals when water interacts with minerals containing aluminum, oxygen, and silicon.

Chemical weathering is accelerated by increased surface area from mechanical weathering.

Acidic waters, such as those containing carbonic acid, speed up chemical weathering.

The rate of weathering is influenced by climate, rock type, and environmental factors.

Erosion is the movement of rock particles by agents like water, wind, glaciers, and gravity.

Deposition occurs when erosional agents lose energy and drop sediments at lower elevations.

Sediments' characteristics can reveal their travel history and maturity.

Sediment transport and deposition processes result in various sediment textures, including graded bedding.

Sediments eventually turn into rocks through compaction or cementation.

Compaction squeezes mud-sized grains, releasing water and causing particles to stick together.

Cementation involves minerals like hematite, calcite, and quartz cementing grains together.

Transcripts

hello grade 11

welcome in this video we will focus our

discussion on the exogenic processes

which include weathering erosion and

deposition now let's get started

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our discussion will focus on the

learning competency

explain how the products of weathering

are carried away by erosion

and deposited elsewhere

at the end of the lesson you should be

able to

1. explain how weathering erosion and

deposition

occur to identify agents of weathering

erosion

and deposition earth's surface

is covered by rocks

these rocks undergo series of geologic

processes

known as the exogenic process

this includes weathering erosion

and deposition now how are these

three processes connected let's start

with weathering

weathering is a process by which rocks

are broken into smaller fragments

chemically or physically

this process is due to rocks exposure to

varying temperature

pressure substances and biological

actions

weathering can either be mechanical or

chemical

[Music]

mechanical weathering happens when a

large rock breaks into pieces physically

without alteration in its chemical

composition

there are a number of ways mechanical

weathering can happen naturally

frost wedging is a process where water

fills cracks or holes in a rock during

the

day and at night freezes since frozen

water has a higher volume than liquid

water

as the ice expands each night it wedges

the cracks or holes open deeper

as rock is broken off pieces fall and

collect at the base of the cliff below

creating a tailless slope a good clue

that frost wedging is happening above

exfoliation is a process where a rock is

unburdened by its overlying rocks during

erosion

the result is a reduction in pressure

under less pressure

the surface of the rock expands outward

and can shed layers like an onion

a form of exfoliation can also happen

when the surface of a rock is heated up

during the day and expands

and then cools at night and contracts

the continual expansion and contraction

can weaken the outer layer of a rock

and make it shed in onion-like layers

mechanical weathering can also be

increased when the roots of trees and

plants grow inside cracks in the rock

and wedge them open larger

tide pool organisms such as sea urchins

can dig holes into a rock and increase

the rate of mechanical weathering

on the other hand chemical weathering

requires chemical reaction

between rock minerals and other

substances in the environment

in order to break rocks three major

types of chemical reactions can occur

during those interactions including

dissolution

oxidation and hydrolysis dissolution

happens when the atomic bonds in glass

or a mineral or shell

are broken by water molecules polar

water molecules will pull apart ions

from solid crystals

and surround those ions in hydration

spheres

these hydration spheres keep the ions

separated so they can't recombine

the ions stay dissolved in the water as

long as there is enough water to keep

them separated

the opposite of dissolution is

precipitation the combining of ions to

form solid crystals that settle out of

water

precipitation happens when waters rich

and dissolved ions evaporate

taking the water molecules away and

allowing the ions to find each other

again

if the water involved with dissolution

is flowing water like rain water or

river water or waves

the dissolved ions will be removed from

the rock and the environment

and taken to a new environment where

precipitation may later happen

as for example a cement between sediment

grains

oxidation happens when oxygen in the

atmosphere gets together with dissolving

ions and creates a new oxide mineral

such as iron oxide or rust this new

oxide will coat the surface of the rock

where the dissolution was taking place

we see evidence of oxidation when we see

stained surfaces on rocks

these stains will come in a multitude of

colors depending on which ion oxidized

iron oxides can be yellow orange red or

brown

depending mostly on how much oxygen is

available

manganese oxides are black copper oxides

are bright blue

iron oxides are the most common oxides

found on the surfaces of rocks

and usually when you see a red colored

rock from a distance you're looking at

the oxide stains on its surface

hydrolysis happens when water interacts

with a mineral that contains aluminum

al oxygen o and silicon si

during dissolution of such a mineral the

water will react with the ingredients to

form a new clay family mineral

for example when potassium feldspar

reacts with water

it forms the clay mineral kaolinite clay

minerals are often white

though they can come in multiple colors

and the crystals that form are

microscopic

so they end up appearing like a fine

powder like grains of flour

this image shows kaolinite the white

powder forming along the edges of an

altered potassium feldspar in a granite

of course as mechanical weathering

increases so too does chemical

weathering

and vice versa chemical weathering

happens faster when there is greater

exposed surface

when rocks break down into smaller

pieces through mechanical weathering

they now have collectively a much

greater surface area

the more chemical weathering that occurs

the more pits and holes in the rocks as

minerals dissolve or turn into easily

eroded clays

which gives more opportunity for things

like frost wedging to occur

another thing that can speed up chemical

weathering are acidic waters

the most common naturally formed acid is

carbonic acid

which forms whenever carbon dioxide

mixes with water

a common occurrence in all natural

waters on earth's surface

this acid is what makes carbonated

beverages acidic

and what can thus increase the acidity

of your stomach when you drink sodas in

high amounts

waters rich in carbonic acid will make

chemical weathering happen faster

what else can speed up any kind of

weathering the rock type and the climate

or environment

minerals with the strongest covalently

bonded silicon oxygen tetrahedra

such as quartz as described already have

the strongest bonds

and are least likely to be dissolved by

water chemical weathering will happen

very slowly with these minerals because

it's so difficult to break through the

bonded tetrahedra both physically and

chemically

on the other hand minerals with weaker

ionic bonds will dissolve more readily

as will minerals with good cleavage so

the minerals in a rock

will determine in large part how fast it

will weather

in addition to the rock type the

environment makes a big difference in

weathering rates

chemical weathering requires water so

the wetter the climate the more chemical

weathering will occur

heat speeds up the rate of chemical

reactions so hot

wet climates have the highest rates of

chemical weathering

cold dry climates like at the poles or

at high elevations

have the slowest rates of chemical

weathering and of course

climates with regular freeze thaw cycles

will have increased rates of frost

wedging

climates with hot days and cool nights

increased rates of

exfoliation the type

extent and rate of weathering are

affected by the following factors

climate rock type rock structure

slope and duration of exposure

[Music]

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now let's discuss erosion and deposition

erosion is the process when rock

particles are moved from one place to

another

as agents of erosion carry the rock

particles they lose energy until such

point that they can no longer hold them

rock sediments are then dropped to

certain locations usually of lower

elevation

this process is called deposition

sediments are dropped off by agents of

erosion

erosion takes place due to the following

agents

water this occurs from the chemicals in

the water

and the force and flow of the water

water runs over the ground

carrying with it rock particles this

surface runoff eventually enters a body

of water such as streams

lakes and oceans

next is wind loose rock and soil

particles are carried away by wind

and are deposited at other places wind

is capable of transporting light

particles

over large areas thousands of kilometers

away

[Music]

glaciers large mass of ice and snow that

forms in colder parts of the world

as glaciers move across land they erode

solid rocks and deposit eroded material

somewhere

and gravity a major force that drives

erosion and deposition

soil and weather materials in high

elevations like kales and mountain

are pulled down by gravity loose rods on

a steep slope may roll downside

and deposit materials at the base

once rocks have weathered the weathered

pieces can collect on earth's surface in

low-lying areas

they can get picked up by the erosional

agents of running water glaciers wind

gravity or humans and moved along to a

new surface where they settle out

during the process of movement it'll

surface the erosional processes

the pieces will continue to break down

chemically and physically

such that after many hundreds of years

and many hundreds of kilometers from

their place of origin what's primarily

left

are the finest sands and muds made of

the most resistant material

the two most abundant minerals that are

found in these long traveled mature

sediment piles

are quartz and clay because

sediment piles will vary around the

planet depending on the materials that

feed into them

they all have a fingerprint a distinct

character of

varying grain compositions sizes shapes

and sorting

we can describe those characteristics

and use them to interpret the travel

history and maturity of the sediment

for example as sediments migrate

downhill towards low-lying areas

especially if carried by running water

they knock about and get smaller and

rounder

if deposited by waves or rivers in the

normal course of movement

they will do so because of gradual

slowing of the water

and thus only grains of the size no

longer able to be carried due to the

drop in velocity

will settle out so all the grains in a

given pile of river sediment

alluvium will be the same size and all

the easily rusted dissolved and

hydrolyzed minerals will be gone

leaving only the most stable ones note

when sediments are transported by

glaciers they are trapped in the ice at

the base of the glacier and so don't

knock about so much

or whether glacial deposits known as

moraines form when glaciers melt and

leave the sediment they carried behind

in one

big pile of unsorted angular grains of

all sizes

very different from river-deposited

sediment

sometimes a flash flood in the mountains

or an avalanche of sediment off the

continental shelf will pick up grains of

all sizes

and then drop them all at the same time

at the foot of the slopes where they hit

the flat valley floor

in these cases as the water movement

stops quickly and the grains settle in

one spot

the largest heaviest grains will settle

out first followed by smaller and

smaller ones

this settling can result in a texture in

the sediment called

graded bedding which if buried by

additional future deposits

can eventually be turned into rock

retaining fossil evidence of the past

graded betting event

ultimately all these described piles of

sediments of varying maturity

will turn themselves into rocks either

through compaction or cementation

compaction happens when mud-sized grains

are squeezed

water is released and the clay particles

within stick together

cementation happens when groundwater's

rich and dissolved ions percolate

through the grains

eventually as the water leaves or

evaporates crystals are left behind

these crystals will grow between and

cement together the grains

examples of common cements include

hematite rust

calcite and quartz

and that ends our lesson congratulations

thank you