CXC/CSEC Geography: Natural Systems

Introduction Plate Tectonics Landforms Weather & Climate Vegetation Soils Natural Hazards Glossary Self-Assessment

Introduction to Natural Systems

Natural systems are the interrelated physical components of our planet that work together to create the environment we live in. These systems include lithosphere (the solid rocky crust), hydrosphere (water bodies), atmosphere (the gaseous layer), and biosphere (living organisms). Understanding these systems is crucial for comprehending the processes that shape our world.

Key Components of Natural Systems

Lithospheric systems: plate tectonics, landform development, rock cycle
Atmospheric systems: weather patterns, climate zones, air circulation
Hydrological systems: ocean currents, river systems, water cycle
Biospheric systems: natural vegetation, soil development, ecosystems

These systems interact continuously through energy and material exchanges, creating dynamic relationships that maintain Earth's balance. For the CXC/CSEC Geography syllabus, we'll explore each of these components in detail, examining how they function individually and as part of the larger natural world.

Plate Tectonics

The Structure of the Earth

The Earth consists of four main layers:

Inner Core: A solid sphere composed primarily of iron and nickel with temperatures similar to the surface of the sun
Outer Core: A liquid layer of iron and nickel surrounding the inner core
Mantle: The thickest layer (approximately 2,900 km), composed of semi-solid rock material
Crust: The thin outer layer of solid rock (5-70 km thick) that forms the continents and ocean floors

Tectonic Plate Theory

The Earth's crust is divided into large segments called tectonic plates that float on the semi-liquid asthenosphere (upper mantle). These plates move due to convection currents in the mantle, creating various geological features where they interact.

Major Tectonic Plates

Pacific Plate
North American Plate
South American Plate
Eurasian Plate
African Plate
Indo-Australian Plate
Antarctic Plate
Caribbean Plate

Types of Plate Boundaries

Convergent Boundaries: Where plates move toward each other, resulting in:
- Oceanic-Continental Collision: Oceanic crust subducts under continental crust, forming deep ocean trenches and volcanic mountain ranges (e.g., Andes Mountains)
- Oceanic-Oceanic Collision: One oceanic plate subducts under another, creating island arcs (e.g., Japanese islands)
- Continental-Continental Collision: Neither plate subducts; instead, they push against each other, creating folded mountain ranges (e.g., Himalayas)
Divergent Boundaries: Where plates move away from each other:
- On land: Creates rift valleys (e.g., East African Rift Valley)
- On ocean floor: Forms mid-ocean ridges where new crust is created (e.g., Mid-Atlantic Ridge)
Transform Boundaries: Where plates slide past each other horizontally, creating fault lines and frequent earthquakes (e.g., San Andreas Fault)

Effects of Plate Movement

Plate movements are responsible for:

Earthquakes: Sudden releases of energy when plates slip past one another
Volcanoes: Formed when molten rock rises through cracks in the Earth's crust
Mountain building: Created by compression, folding, and uplift of crustal material
Continental drift: The gradual movement of continents over geological time

Caribbean Context: The Caribbean region sits primarily on the Caribbean Plate, which interacts with the North American, South American, and Cocos plates. This tectonic setting explains the volcanic activity in the Lesser Antilles (eastern Caribbean) and the earthquake vulnerability throughout the region.

Landforms and Geomorphic Processes

The Rock Cycle

The rock cycle is the continuous process by which rocks change from one type to another over time through various geological processes:

Igneous rocks: Formed from the cooling and solidification of magma or lava (e.g., basalt, granite)
Sedimentary rocks: Formed from the compaction and cementation of sediments (e.g., limestone, sandstone)
Metamorphic rocks: Formed when existing rocks are subjected to intense heat and pressure (e.g., marble, schist)

Weathering Processes

Weathering is the breakdown of rocks in situ (without movement) due to exposure to the atmosphere:

Physical (Mechanical) Weathering:
- Freeze-thaw action: Water expands when frozen, creating pressure that cracks rocks
- Exfoliation: Peeling of rock layers due to pressure release
- Temperature changes: Expansion and contraction causing rock fracture
- Biological activity: Plant roots growing into cracks
Chemical Weathering:
- Oxidation: Reaction with oxygen (rusting of iron-bearing minerals)
- Carbonation: Reaction with carbonic acid (dissolution of limestone)
- Hydrolysis: Breakdown of minerals when they react with water
- Solution: Dissolution of soluble minerals in water
Biological Weathering:
- Plant growth: Roots widening cracks
- Burrowing animals: Creating pathways for water and air
- Microbial action: Breaking down minerals

Caribbean Context: In the Caribbean, chemical weathering is especially significant due to the hot, humid climate. Carbonation is particularly important in areas with limestone bedrock, such as parts of Jamaica, which has developed extensive karst landscapes with sinkholes, caves, and disappearing streams.

Erosion and Transport Processes

Erosion is the removal and transportation of weathered material by agents such as:

Water erosion: Rivers, waves, rainwater
Wind erosion: Particularly significant in arid regions
Glacial erosion: Movement of ice masses
Gravity: Mass movements such as landslides and rockfalls

Fluvial (River) Landforms

Rivers create distinctive landforms as they travel from source to mouth:

Upper Course

V-shaped valleys: Formed by vertical erosion
Waterfalls and rapids: Form where resistant rock overlies less resistant rock
Gorges: Deep, narrow valleys with steep sides
Interlocking spurs: Projections of higher land that appear to interlock

Middle Course

Wider, flatter valleys: Lateral erosion becomes more important
Meanders: Winding curves in the river channel
River cliffs and slip-off slopes: Formed by erosion on outer bends and deposition on inner bends
Oxbow lakes: Formed when a meander is cut off from the main channel

Lower Course

Floodplains: Flat areas beside rivers that flood periodically
Levees: Natural embankments formed during flooding
Deltas: Depositional features at river mouths (e.g., Mississippi Delta)
Estuaries: Tidal river mouths (e.g., Amazon Estuary)

Coastal Landforms

Coastal areas feature distinctive landforms created by wave action, tides, and currents:

Erosional Features

Cliffs: Steep rock faces created by wave erosion at the base
Wave-cut platforms: Flat areas left when cliffs retreat
Caves, arches, stacks: Progressive erosion of headlands
Blow holes: Vertical shafts formed when sea caves extend upward

Depositional Features

Beaches: Deposits of sand or pebbles
Spits: Elongated deposits of sand extending from the coast
Tombolas: Deposits connecting an island to the mainland
Barrier islands: Offshore deposits parallel to the coast

Karst Landscapes

Karst landscapes develop in regions with soluble rocks (usually limestone) and are characterized by:

Sinkholes (dolines): Surface depressions caused by collapse or dissolution
Caves and caverns: Underground chambers formed by dissolution
Stalactites and stalagmites: Mineral deposits in caves
Disappearing streams: Rivers that flow underground through sinkholes
Limestone pavements: Exposed rock surfaces with dissolution features

Caribbean Context: The Cockpit Country in Jamaica is one of the world's most distinctive karst landscapes, featuring conical hills, deep depressions, caves, and underground rivers. The region is crucial for Jamaica's water supply, as much of the island's water filters through this limestone region.

Weather and Climate

Elements of Weather and Climate

Temperature: Measure of heat energy in the atmosphere
Precipitation: Water falling from clouds as rain, snow, sleet, or hail
Humidity: Amount of water vapor in the air
Air pressure: Force exerted by the weight of air
Wind: Horizontal movement of air
Cloud cover: Proportion of sky covered by clouds
Sunshine: Duration and intensity of solar radiation

Weather vs. Climate: Weather refers to the short-term atmospheric conditions at a specific place and time. Climate refers to the long-term (typically 30+ years) average weather patterns in a region.

The Atmosphere

The atmosphere is divided into layers based on temperature differences:

Troposphere: Lowest layer (0-12 km), where all weather occurs
Stratosphere: (12-50 km) Contains the ozone layer
Mesosphere: (50-80 km) Where most meteors burn up
Thermosphere: (80-700 km) Where auroras occur
Exosphere: (700+ km) Outermost layer, merges with space

Global Atmospheric Circulation

The atmosphere circulates in a pattern of cells driven by solar heating and the Earth's rotation:

Hadley Cells: Located between the equator and 30° N/S
Ferrel Cells: Located between 30° and 60° N/S
Polar Cells: Located between 60° and 90° N/S

These cells create global wind belts:

Trade Winds: From 30° N/S toward the equator
Westerlies: From 30° to 60° N/S
Polar Easterlies: From the poles to 60° N/S

Factors Affecting Climate

Latitude: Determines the angle of the sun's rays and day length
- Equatorial regions (0°): High temperatures year-round with little seasonal variation
- Tropical regions (0°-23.5°): Hot with distinct wet and dry seasons
- Temperate regions (23.5°-66.5°): Moderate temperatures with four distinct seasons
- Polar regions (66.5°-90°): Cold year-round with extreme seasonal variations in daylight
Altitude: Temperature decreases by approximately 6.5°C per 1,000 meters of elevation
Distance from the sea:
- Maritime climate: Moderate temperatures with lower annual temperature range
- Continental climate: More extreme temperatures with higher annual temperature range
Ocean currents:
- Warm currents: Increase temperatures and moisture in adjacent land areas
- Cold currents: Decrease temperatures and often create arid conditions
Prevailing winds: Influence temperature and precipitation patterns
Relief (mountains):
- Rain shadow effect: Dry conditions on the leeward side of mountains
- Orographic rainfall: Increased precipitation on the windward side
Vegetation cover: Affects local temperature and humidity
Human activities: Urbanization, deforestation, pollution affecting local and global climate

Major Climate Types (Köppen Classification)

Climate Type	Characteristics	Locations
Tropical Rainforest (Af)	Hot and wet year-round; daily rainfall; little seasonal variation	Amazon Basin, Congo Basin, Southeast Asia, Caribbean islands
Tropical Monsoon (Am)	Hot with distinct wet and dry seasons influenced by seasonal winds	India, Southeast Asia, Northern Australia
Tropical Savanna (Aw)	Hot year-round with pronounced wet and dry seasons	Sub-Saharan Africa, Central Brazil, Northern Australia
Desert (BWh)	Hot days, cold nights; minimal precipitation; high evaporation	Sahara, Arabian, Australian deserts
Mediterranean (Csa)	Hot, dry summers; mild, wet winters	Mediterranean Basin, California, Central Chile, South Africa
Humid Subtropical (Cfa)	Hot, humid summers; mild winters; year-round precipitation	Southeastern USA, Eastern China, Eastern Australia
Marine West Coast (Cfb)	Mild temperatures; year-round precipitation; cloudy	Western Europe, New Zealand, Pacific Northwest USA
Humid Continental (Dfb)	Warm summers; cold, snowy winters; large annual temperature range	Northeastern USA, Eastern Europe, Northern Asia
Subarctic (Dfc)	Short, cool summers; long, severe winters; permafrost	Northern Canada, Alaska, Siberia
Tundra (ET)	Very short growing season; cold all year; permafrost	Arctic regions, high mountain areas

Caribbean Context: The Caribbean region primarily has a tropical climate, but with variations. The climate can be classified as tropical rainforest (Af) in areas with high rainfall throughout the year, or tropical monsoon (Am) and tropical savanna (Aw) in areas with more pronounced wet and dry seasons. Local variations occur due to differences in elevation, exposure to prevailing winds, and island size.

Weather Systems and Phenomena

Tropical Cyclones (Hurricanes)

Tropical cyclones are intense low-pressure systems that form over warm tropical waters (above 26°C) and are characterized by:

Circular organization of thunderstorms around a central "eye"
Strong winds (sustained winds of at least 74 mph/119 km/h for hurricanes)
Heavy rainfall that can cause flooding
Storm surges that can inundate coastal areas

Hurricane formation requires:

Warm ocean waters (above 26°C)
Atmospheric instability
High humidity in the lower and middle troposphere
Sufficient Coriolis force (typically at least 5° away from the equator)
Pre-existing near-surface disturbance
Low vertical wind shear

The Inter-Tropical Convergence Zone (ITCZ)

The ITCZ is a belt of low pressure near the equator where the trade winds converge. It is characterized by:

Rising air creating cloudy, rainy conditions
Seasonal movement north and south following the sun's zenith position
Influence on wet and dry seasons in tropical regions

El Niño-Southern Oscillation (ENSO)

ENSO is a climate pattern involving temperature changes in the central and eastern tropical Pacific Ocean:

El Niño: Warmer-than-average sea surface temperatures, affecting global weather patterns
La Niña: Cooler-than-average sea surface temperatures, generally causing opposite effects to El Niño
Effects: Changes in precipitation patterns, ocean temperatures, and marine ecosystems globally

Vegetation and Ecosystems

Major World Biomes

Biomes are large regions with similar climate, vegetation, and wildlife:

Biome	Climate	Vegetation Characteristics	Locations
Tropical Rainforest	Hot, wet year-round	Dense evergreen vegetation; tall trees; multiple canopy layers; high biodiversity	Amazon Basin, Congo Basin, Southeast Asia, Caribbean islands
Tropical Savanna	Hot year-round with wet/dry seasons	Grasses with scattered drought-resistant trees; fire-adapted vegetation	Sub-Saharan Africa, Northern Australia, Central Brazil
Desert	Hot days, cold nights; minimal rainfall	Sparse vegetation; succulents; drought-resistant shrubs; ephemeral plants	Sahara, Arabian Desert, Sonoran Desert
Mediterranean	Hot, dry summers; mild, wet winters	Drought-resistant woody shrubs; evergreen trees with hard leaves	Mediterranean Basin, California, Chile
Temperate Deciduous Forest	Four distinct seasons	Deciduous trees that shed leaves in winter; moderate biodiversity	Eastern North America, Western Europe, East Asia
Temperate Grassland	Hot summers, cold winters; moderate rainfall	Dominated by grasses; few trees; deep, fertile soil	North American prairies, Eurasian steppes, South American pampas
Taiga (Boreal Forest)	Long, cold winters; short summers	Coniferous evergreen trees; low biodiversity	Northern North America, Scandinavia, Siberia
Tundra	Very cold; short growing season	No trees; mosses, lichens, small shrubs; permafrost	Arctic regions, high mountain areas

Tropical Rainforest Characteristics

The tropical rainforest is particularly important in the Caribbean context:

Structure:
- Emergent layer: Scattered very tall trees (45-55m) that poke above the canopy
- Canopy layer: Dense layer of overlapping treetops (30-45m)
- Understory: Smaller trees and shrubs adapted to low light (5-30m)
- Forest floor: Limited vegetation due to low light levels
Adaptations of vegetation:
- Drip tips on leaves to shed excess water
- Smooth, thin bark on trees
- Buttress roots for support in shallow soils
- Epiphytes growing on other plants to access light
- Lianas (woody vines) climbing trees to reach the canopy
Biodiversity: Highest biodiversity of any biome, containing more than half of all known plant and animal species

Vegetation Succession

Vegetation succession is the gradual change of plant communities over time:

Primary succession: Development of vegetation on previously unvegetated land (e.g., newly formed volcanic islands, areas exposed after glacial retreat)
Secondary succession: Redevelopment of vegetation on disturbed land where soil remains (e.g., after forest clearing, fire, or abandonment of agricultural land)
Climax community: The stable end stage of succession, which is in equilibrium with the local environment

Stages of secondary succession in a tropical environment:

Pioneer species (grasses, ferns, fast-growing shrubs)
Early successional species (sun-loving trees and shrubs)
Mid-successional species (more diverse tree community)
Late successional species (shade-tolerant trees)
Climax community (fully developed, self-sustaining forest)

Human Impact on Vegetation

Human activities significantly affect natural vegetation through:

Deforestation: Clearing forests for agriculture, timber, mining, or development
Agriculture: Converting natural ecosystems to cropland or pasture
Urbanization: Replacing natural areas with built environments
Introduction of invasive species: Non-native plants outcompeting native vegetation
Climate change: Altering temperature and precipitation patterns, affecting plant distributions
Fragmentation: Breaking continuous habitat into isolated patches

Caribbean Context: The Caribbean islands have experienced significant vegetation changes since European colonization. Primary forests have been cleared for sugarcane, banana, and coffee plantations. Today, many islands have a mix of cultivated land, secondary forest, and fragments of primary forest in protected areas. Unique ecosystems include mangrove forests along coastlines, which provide crucial habitat and coastal protection.

Soils

Soil Formation (Pedogenesis)

Soil formation is influenced by five main factors:

Parent material: The original rock or deposit from which soil develops
Climate: Temperature and precipitation affecting weathering rates and organic matter decomposition
Living organisms: Plants, animals, bacteria, and fungi influencing soil formation
Topography: Slope angle and aspect affecting drainage and erosion
Time: Duration of soil-forming processes

Soil Profiles and Horizons

A soil profile is a vertical section through the soil showing distinct layers called horizons:

O horizon: Surface layer of organic material (leaf litter, decomposing matter)
A horizon: Topsoil with high organic content, site of most biological activity
E horizon: Zone of leaching (eluviation) where materials move downward
B horizon: Subsoil where materials accumulate (illuviation)
C horizon: Partially weathered parent material
R horizon: Bedrock

Natural Hazards

Natural hazards related to soil include:

Landslides: Triggered by soil saturation, erosion, or seismic activity.
Soil erosion: Loss of topsoil due to wind/water, reducing fertility.
Expansive soils: Clay-rich soils that swell with water, damaging structures.
Desertification: Soil degradation in arid regions due to drought or overuse.

Glossary

Eluviation: Leaching of minerals/nutrients from upper soil layers.
Illuviation: Deposition of leached materials in lower horizons (e.g., B horizon).
Parent material: Unweathered geologic material from which soil forms.

Self-Assessment

1. Which soil horizon is most affected by leaching?

2. What is the primary difference between the A and B horizons?

3. How can expansive soils become a natural hazard?

4. Why is the O horizon crucial for soil ecosystems?

5. What process dominates the B horizon, and how does it differ from the E horizon?

6. How does desertification relate to soil horizons?

7. Which soil horizon would you expect to find bedrock fragments transitioning into solid rock?

8. How might human activities accelerate soil erosion?

9. What role does the C horizon play in soil formation?

10. Why might landslides occur more frequently in areas with steep slopes and thick E horizons?

11. How does the presence or absence of an O horizon indicate soil health?

12. What engineering challenges might the B horizon pose for construction?