GY1004 Principles of Physical Geography B Dr Mark Powell Room F44 [email protected] DEPARTMENT OF GEOGRAPHY.

GY1004 Principles of Physical Geography B

Dr Mark PowellRoom F44

[email protected]

DEPARTMENT OF GEOGRAPHY

GY1003

GY1004 Part 1 (Weeks 1-5) Weathering, Soils and

Landscape

Weathering

Pedogenesis

Denudation

Global scalevariations

Weathering, Soils and Landscape

WeatheringRocks and mineralsPhysical weathering processesChemical weathering processesWeathering products and

process controls

Weathering, Soils and Landscape

SoilsThe soil system and soil

propertiesSoil processes, types and

patterns

Weathering, Soils and Landscape

Erosion and LandscapeAgents and landscapes of

erosion and depositionRates of denudationUplift and denudation

Multiple Choice test based on Lectures 1-10

Monday 1st March 2004

PowerPoint presentations can be viewed at

www.geog.le.ac.uk/staff/dmp6/teaching

Weathering: An introduction

Weathering - The chemical alteration and physical breakdown of rock material at or near the earth’s surface.

The significance of weathering

Weathering is often a precursor to erosion by rivers, winds, glaciers and mass movements

Geomorphologists study the development of landscapes and are concerned with rates of weathering processes, the nature of the weathered material and the landforms that result

The significance of weathering

Weathering also gives rise to specific landforms

Bornhardts, Rio

Karst, China

Finger of God, Namibia

The significance of weathering

Weathering produces regolith, the parent material of soils.

Soil scientists are interested in the way weathering contributes to soil properties and the release and movement of nutrients

A terra rossa soil

Weathering

1) Rocks and minerals

2) Chemical weathering processes

3) Physical weathering processes

4) Weathering products and process controls

Lecture 1 Rocks and minerals

Minerals – the building blocks of rocks

The atomic structure of matter

Rock forming minerals

Rocks and rock types

What is a mineral?A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition.

Must be found in nature

A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition.

Atoms are arranged in an orderly, repeated 3d array

A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition.

Excludes organic substances that make up plant and animal bodies

A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition.

The combination of its chemical composition and the arrangement of its atoms in its internal structure makes each mineral unique

A naturally occurring solid crystalline, generally inorganic substance with a specific chemical composition.

Olivine

Quartz

What is a rock?

Rocks are made up of varying assemblages of minerals

Minerals, therefore, are the building blocks of rocks

CalciteLimestone outcrop

El Torcal de Antequera, Spainorthoclase plagioclase

quartzhornblende

biotite

Granite

The minerals of Granite

Elements and atoms

Elements are the most fundamental substances into which matter can be separated and analysed by ordinary chemical means

An atom is the smallest unit of an element that retains the physical and chemical properties of that element.

Eight most abundant elements in Earth’s crust -

oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium.

The structure of the atom

Protons

Neutrons

Electrons

Charge

+1

0

-1

Mass

1

1

1/1836

Atomic number, atomic mass and isotopes

Atomic number (Z) – the number of protons in the nucleus of an atom

Hydrogen (Z = 1)

Carbon (Z = 6)

Atomic number, atomic mass and isotopes

Atomic mass (mass number; A) is the mass of the atom. It is equal to the number of protons and neutrons in the nucleus.

Hydrogen (A = 1)

Atomic number, atomic mass and isotopes

Atomic number, atomic mass and isotopes

Atomic number, atomic mass and isotopes

Atomic number, atomic mass and isotopes

Isotopes are elements with different numbers of neutrons in the nucleus. Isotopes have the same atomic numbers (no. of protons), but different mass numbers (numbers of protons and neutrons).

Protons Neutrons

Carbon 12 6 6

Carbon 13 6 7

Carbon 14 6 8

Why do minerals form?

Na

Cl

Sodium atom:1 electron inouter shell

Chlorine atom:7 electrons inouter shell

Chemicalreaction

Na+

Cl-

Sodium loses 1 electronto become sodium ion

Chlorine gains 1 electronto become chlorine ion

Electricalattraction

Cl-

Na+

Compound, sodium chloride (NaCl), formed by electrical attraction between Na+ and Cl-

Chemical bonds

Electrical forces of attraction between electrons and protons

IONIC – between ions of opposite charge - most common mineral bond

COVALENT – between ions that share electrons - stronger than ionic bonds

How do minerals form?E.g. Diamond

How do minerals form?E.g. Diamond

How do minerals form?

E.g. Diamond

When do minerals form?

Temperatures below freezing/melting points

Precipitation during evaporation

Rock forming mineralsSilicates - the most abundant and important

rock forming mineral- composed of oxygen and silicon

mostly in combination with the cations of other elements (e.g. Na, Ca, Mg, K)

orthoclase plagioclase

quartzhornblende

biotite

Rock forming minerals

Carbonates- minerals made up of carbon and oxygen in the form of the Carbonate ion (CO3) and in combination with calcium and magnesium

Calcite

Rock forming minerals

Oxides- compounds of oxygen and metallic cations such as hematite (Fe2O3 – iron oxide)

Hematite

Rock forming minerals

Sulphides and sulphates

- compounds of the sulphide (S2-) and

sulphate (SO4-) ion e.g. iron pyrite (FeS2

fools gold) and anhydrite (CaSO4)

iron pyrite anhydrite

Rocks and rock properties

Texture – the sizes, shapes and spatial arrangement of its crystals and grains

Mineralogy – the kinds and proportions of the minerals that make up the rock

Igneous rocksCommon minerals

*Quartz*Feldspar*Mica*Pyroxene*Amphibole*Olivine

* silicate minerals

Crystals form fromMagma cooling andsettle to floor of chamber

Crystals from earlycooling accumulate

Weathering anderosion

Sedimentary rocks

Burial and lithificationinto sedimentary rock

Ocean transport anddeposition by currentsand chemical precipitation

Land transport and depositionby water, wind, ice

Sedimentary rocks

Chemical – calcite, gypsum, halite

Biogenic – limestone, dolomite, chert

Clastic – sandstones, mudstones and conglomerates

silicates, e.g. quartz, clay minerals and feldspar

carbonates, sulphates and chlorides

carbonates

Lithification – compaction and cementation

Metamorphic rocks

SUMMARYMinerals

Minerals are the building blocks of rocks

Minerals are naturally inorganic solids with specific crystal structures and chemical compositions.

There are about 3500 minerals, but about 30 are responsible for about 99% of the volume of the earth’s crust.

SUMMARYThe atomic structure of

matter

Minerals are constructed of atoms, the small units of matter that combine in chemical reactions

An atom is composed of a nucleus of protons and neutrons surrounded by electrons travelling in orbitals (shells) around the nucleus.

The atomic number of an element is the number of protons in its nucleus

The atomic mass of an element is the sum of the masses of its protons and neutrons.

When an mineral crystallises, atoms or ions come together in the proper proportions to form a crystal structure – an orderly three dimensional geometric array in which the basic arrangement is repeated in all directions.

SUMMARYHow do minerals form?

Chemical substances react with each other to form compounds either by gaining or losing electrons to become ions or by sharing electrons.

Either way, the atoms achieve stable configurations of electron shells.

The atoms or ions of a mineral are held together by ionic or covalent bonds

SUMMARYThe rock forming minerals

Silicates are the most abundent minerals in the Earth. They are composed of tetrahedra of silicon and oxygen atoms linked in various ways

Carbonate minerals are made up of carbonate ions bonded to calcium and/or magnesium.

Oxide minerals are compounds of oxygen and metallic elements.

Sulphate and sulphide minerals are structures made up of sulphur atoms in combination with metallic elements.

SUMMARYRocks

Rock properties are defined by mineralogy (the kinds and proportions of the constituent minerals) and texture (the sizes, shapes and spatial arrangement of its crystals or grains).

The mineralogy and texture of a rock are determined by the geologic conditions, including chemical composition, under which it formed

Igneous rocks are formed by the crystallisation of magma as it cools;

Sedimentary rocks are formed by the lithification of sediments/precipitates;

Metamorphic rocks are formed by the alteration in the solid state of igneous, sedimentary or other metamorphic rocks by heat and or pressure.