University Geography: Comprehensive Academic Notes on Earth Systems and Global Challenges

What are Natural Hazards?

• Definition: A natural process that could cause loss of life or damage to property. A phenomenon is only a hazard if it threatens humans. Example: An earthquake on a remote, uninhabited island is not a hazard.
• Tectonic Hazards (楄造灰倳): Caused by endogenetic crustal movement. Examples: Earthquakes, volcanic eruptions, tsunamis.
• Climatic Hazards (我候灰倳): Caused by climatic extremes. Examples: Flooding, drought, typhoons (hurricanes), tornadoes, heat waves, cold surges, blizzards, wildfires, hailstones.
• Geomorphic Hazards (地耐灰倳): Processes occurring on the land surface. Examples: Landslides, mudflow, avalanches.
• Biological Hazards (生物灰倳): Caused by living organisms/diseases. Examples: Viruses, infections, pests (e.g., locusts).

Internal Structure and Chemical Composition of Earth

• Crust (地殼): The solid outer layer, thinnest and least dense, mainly silica.
  • Continental Crust (Sial): Rich in Silicon ($Si$) and Aluminum ($Al$). Mostly granitic rocks. Thickness: $30-50\,km$. Density: $2.7\,g/cm^3$. Discontinuous layer, older rocks.
  • Oceanic Crust (Sima): Rich in Silicon ($Si$) and Magnesium ($Mg$). Mostly basaltic rocks. Thickness: $5-10\,km$. Density: $3.0\,g/cm^3$. Continuous layer, younger rocks. It subducts into the asthenosphere because it is denser.
• Mantle (地幔): Thickness over $2500\,km$. Rich in Iron ($Fe$) and Magnesium ($Mg$). Temperature: $2500^{\circ}C$. Consists of the upper mantle (uppermost solid mantle + plastic asthenosphere) and a solid lower mantle.
• Core (地核): Hottest ($4000^{\circ}C$) and densest part ($10-13.5\,g/cm^3$). Mostly Iron ($Fe$) and Nickel ($Ni$).
  • Outer Core: Liquid state due to high heat.
  • Inner Core: Solid state due to extreme pressure.

Physical Layers and Plate Tectonics

• Lithosphere (岰石圈): Outermost solid part consisting of the crust and uppermost mantle. Broken into pieces called plates.
• Asthenosphere (軟流圈): Semi-molten/plastic layer below the lithosphere. Convection currents here drive plate movement.
• Plate Types:
  • Continental Plate: Contains both continental and oceanic crusts (e.g., Eurasian, African plates).
  • Oceanic Plate: Consists only of oceanic crust (e.g., Pacific, Nazca plates).
• Movement Mechanisms:
  • Convection Currents: Heat transfer where mantle materials rise near the core and sink when cooled.
  • Ridge Push (脊推): Gravity-driven pushing force from ridges.
  • Slab Pull (板拉): Gravity-driven pulling force from subducting oceanic crust along convergent boundaries.
• Movement Rate: Roughly the speed of fingernail growth (measured via GPS in fractions of a millimeter per year).
• History: Alfred Wegener proposed "Continental Drift" in 1912 ($200$ million years ago, supercontinent Pangaea began breaking apart).

Plate Boundaries and Resultant Landforms

• Divergent / Constructive Boundaries (分向性): Tensional force. Plates move apart. New crust/igneous rocks (Granite, Basalt) formed.
  • Oceanic-Oceanic (O+O): Mid-oceanic ridges (Mid-Atlantic Ridge, East Pacific Rise), rift valleys, volcanic islands (Iceland, Easter Island). Sea floor spreading occurs.
  • Continental-Continental (C+C): Rift valleys (East African Rift Valley), volcanoes (Mt. Kenya, Mt. Kilimanjaro - highest in Africa). Central block sinks between normal faults.
• Convergent / Destructive Boundaries (聚合性): Compressional force. Plates collide and crust is destroyed.
  • Continental-Oceanic (C+O): Denser oceanic crust subducts. Features: Ocean trenches (Peru-Chile Trench), fold mountains (Andes), volcanoes (Mt. Chimborazo), reverse faults.
  • Oceanic-Oceanic (O+O): Forms volcanic island arcs (Japan, Philippines, Indonesia), deep trenches (Japan Trench, Java Trench, Mariana Trench - Challenger Deep is $10971\,m$ deep).
  • Continental-Continental (C+C): No subduction (equal density). Features: Fold mountains (Himalayas - Eurasian vs Indo-Australian; Alps - Eurasian vs African), reverse faults, intrusive vulcanicity (hot springs in Tibet).
• Transform / Conservative Boundaries (轉換): Shear stress. Plates slide past laterally. No new crust formed/destroyed. Features: Transform faults (San Andreas Fault). High seismic risk (1906 San Francisco Earthquake, Haiti 2010 M7.0, Lituya Bay 1958 M8.3).
• Hotspots: Areas of hot mantle plumes away from boundaries. Example: Hawaii. Pacific plate moves NW over a fixed hotspot, creating a chain of volcanoes (oldest NW, youngest SE).

Living in Hazard-Prone Areas: Opportunities vs. Risks

• Opportunities (Reasons to Stay):
  • Fertile Soil: Volcanic ash/basic lava provide nutrients (e.g., rice at Mt. Mayon, Philippines). Supports 1 in 10 global people despite volcanic soil being $< 1\%$ of land.
  • Minerals: Deposits like Sulphur (Kawah Ijen, Indonesia) and precious stones for industry.
  • Energy: Geothermal power (Iceland: $30\%$ of total energy, $85\%$ of houses heated).
  • Tourism: Scenic fold mountains and hot springs (Canary Islands, Bali, Blue Lagoon in Iceland). Over $100$ million visit volcanic sites annually.
  • Social/Economic factors: Long history, job opportunities (miners, guides), high income, social ties, inertia (habit), and poverty (too poor to move).
• Risks (Reasons to Leave):
  • Disasters: Fear of eruption, earthquake, tsunami (injury, death, economic loss).
  • Negative Impact: Mudflows, landslides, poisonous gases (Hydrogen Sulphide), acid rain.
  • Governance: Low confidence in rescue work or government efficiency.

The Water Cycle and Drainage Basins

• Inputs: Precipitation (Rain, snow, sleet, hail).
• Transfers/Processes:
  • Interception: Vegetation trapping water.
  • Infiltration: Water seeping into soil.
  • Percolation: Water moving down into rocks.
  • Surface Runoff: Overland flow + Channel flow.
  • Throughflow: Downslope flow within soil.
  • Groundwater / Base Flow: Downslope flow in rock structure.
• Outputs: Evaporation (water bodies), Transpiration (plants), Evapotranspiration.
• Factors Affecting Infiltration: Decreased by high rainfall intensity and steep gradients; Increased by vegetation and high rock permeability (porosity).
• Drainage Basin Terms: Watershed (boundary), Tributary (small stream), Confluence (meeting point), Distributary (branching off at delta).
• Stream Order: First-order (headwater). Two 1st-order meet to form a 2nd-order. Higher orders mean larger discharge.
• Drainage Density: Total length of channels per unit area. High density caused by high rainfall, steep slopes, and impermeable rock.
• Patterns: Dendritic (tree-like, uniform rock), Rectangular (right angles, faults), Trellis (alternating rock resistance), Centennial (center toward lake), Radial (from center/peak).

Fluvial Processes and River Energy

• Energy Factors: Discharge ($Q$) and Velocity ($V$). Unit for Q: $m^3/sec$. Unit for V: $m/sec$.
• Formula: $Q\, (m^3/sec) = Width\, (m) \times Mean\, Depth\, (m) \times Velocity\, (m/sec)$.
• Friction: Measured by wetted perimeter. Smooth channels (lower course) have high velocity; rough channels (upper course with big boulders) have low velocity.
• Erosion Types:
  • Hydraulic Action: Force of running water.
  • Abrasion: Load rubbing against bed/banks.
  • Attrition: Rocks colliding and breaking.
  • Solution: Soluble minerals dissolved.
• Erosion Locations: Headward (at source), Vertical (deepening - upper course), Lateral (widening - middle/lower course).
• Transportation Types: Traction (rolling bed load), Saltation (bounce), Suspension (silt/clay), Solution (dissolved minerals).
• Deposition: Occurs when energy drops (e.g., river mouth, inner bends). Involves Sorting: Large particles deposited first, small ones further away.

River Characteristics Downstream (Upper to Lower Course)

• Discharge: Increases (larger catchment, more tributaries).
• Velocity: Increases (smoother bed, less friction, larger volume).
• Gradient/Altitude: Decreases.
• Roughness: Decreases (abrasion/attrition round out load).
• Load Size: Decreases; Load Amount: Increases.
• Sinuosity: Increases (more pronounced meandering).
• Channel Shape: Changes from deep V-shaped (upper) to wide asymmetrical (middle) to very wide (lower).

Fluvial Landforms

• Upper Course (Erosional): Interlocking spurs (zig-zag around resistant hills), waterfalls and plunge pools (differential erosion of caprock), gorges (retreating waterfalls).
• Middle Course (Both): Meanders (erosion at outer bank/river cliff, deposition at inner bank/slip-off slope).
• Lower Course (Depositional): Oxbow lakes (cut-off meander loops), floodplains and natural levees (built by repeated silt deposits during floods), braided streams (split by dry-season sediment ridges), deltas (alluvial platforms at river mouth).
• Delta Formation Conditions: Rate of deposition > Removal. Factors: Large load supply, gentle offshore gradient, shallow water, weak tides/currents, presence of vegetation (mangroves).

River Management: Hard and Soft Strategies

• Hard Strategies (Engineered structures):
  • Channelization: Straightening (reduces friction, increases velocity), deepening/widening (increases capacity), concrete lining (prevents erosion).
  • Dredging: Removing sediment to restore capacity.
  • Dykes/Embankments: Raising banks to contain higher discharge.
  • Bypass Floodway: Diverting water (e.g., Yuen Long Bypass Floodway catches $40\%$ runoff).
  • Village Flood Pumping Scheme: For low-lying areas (San Tin).
  • Storage Tanks: Underground storage (Tai Hang Tung: $100000\,m^3$, Happy Valley: $60000\,m^3$).
• Soft Strategies (Working with nature):
  • Land Use Management: Restriction of development on floodplains (land use zoning).
  • Afforestation: Planting trees to increase interception/reduce silting.
  • Warning Systems: Monitoring water levels (HK Observatory Special Announcement).
• River Revitalization: Green channelization elements like gabion banks, fish shelters (holes for refuge), and fish ladders (boulders allowing organism passage).

Industrial Systems and Classification

• Manufacturing System: Inputs (Raw materials, land, labor, capital, power) -> Processes (Spinning, assembly, R&D) -> Outputs (Finished goods, industrial waste).
• Industry 1.0 to 4.0: Water/Steam (1750s) -> Electricity/Mass Production (1870s) -> IT/Automation (1970s) -> Smart Systems/Internet of Things (2011).
• Types:
  • Processing: Raw material to other products (Iron and Steel).
  • Fabricating: Combining parts to finished product (IT, Cars).
  • Heavy: Large inputs/outputs, capital-intensive (Shipbuilding).
  • Light: Small inputs/outputs, labor-intensive.
  • Orientations: Raw material-oriented (Sugar), Power-oriented (Aluminum smelting), Market-oriented (Bakery, Perishables), Footloose (IT).

Case Study: Iron and Steel Industry in China

• Pre-1950s: Clustered in NE China (Anshan) due to proximity to coal (Fushun) and iron ore.
• 1950s-1970s (Inland Shift): Driven by Five-Year Plans for strategic safety and regional balance. New plants in Baotou, Wuhan, Panzhihua.
• 1980s-2000s (Coastal Shift): Market-oriented shift under Reform and Opening Up. Baoshan (Baosteel) in Shanghai at port location. Factors: Import of high-grade ore, scrap iron use, large city markets.
• Since 2000s: "Go West" policy to develop Central Asia markets; and relocation for environmental reasons (Shougang moved from Beijing to Caofeidian to reduce smog for 2008 Olympics).

Case Study: Information Technology (IT) Industry

• Characteristics: High value-added, light nature, short product life cycle, R&D-intensive.
• Multi-Point Production: (1) Headquarters/R&D in MDCs (Silicon Valley) near universities/venture capital. (2) High-end component manufacturing in MDCs/NICs (Taiwan - TSMC, chips; South Korea). (3) Assembly/Low-end components in LDCs (Zhengzhou - "iPhone City", India, Vietnam) for cheap labor and growing markets.
• Global Supply Chain: iPhone example—Designed in California, chips from Taiwan, assembled in China/India.
• Trend: Reshoring: Moving production back to MDCs (USA) to protect intellectual property, reduce supply chain vulnerability, and use automation to offset lower productivity labor gaps.

Urbanization and Building Sustainable Cities

• Settlement Patterns: Dispersed (farms), Linear (Discovery Bay), Nucleated (Fairview Park).
• Urbanization Level: $Urban\, Pop / Total\, Pop \times 100\%$.
• Cycle: Urbanization -> Suburbanization -> Counter-urbanization -> Reurbanization.
• Hong Kong Urbanization: Suburbanization since 1973 (New Town Development). Progressed through three generations of new towns (e.g., 1st: Sha Tin; 2nd: Yuen Long; 3rd: Tung Chung). Currently $9$ new towns house $3.57$ million people ($48\%$ of HK total).
• Urban Problems: Housing shortage (Nano flats), substandard conditions (Urban decay, subdivided flats), traffic congestion (Central CBD peak hours).
• Urban Renewal (5Rs): Redevelopment, Rehabilitation, Preservation, Revitalization, Retrofitting.
• Sustainable City/Compact Urban Form: Balance between Economy, Social progress, and Environment. Efficient land use, smart green transport (MTR-oriented), e-buildings (solar power, vertical greening), and biodiversity conservation (Country parks cover 40% of HK).

Combating Famine

• Types: Under-nourishment, Malnutrition, Famine (extreme shortage).
• Sahel (LDCs): Physical constraints (drought, infertile soil). Human factors (rapid population growth, overgrazing). Practices Nomadic Herding (extensive, transhumance). Measures: sustainable techniques like semi-circular bunds to harvest rain.
• Southern California (MDCs): Mediterranean climate (dry summer). Overcomes constraints via Capital/Technology: Irrigation (Central Valley Project, CVP), Biotechnology (GM crops), Precision Farming (GPS, sensors).
• Sustainable Agriculture Methods: Cropping systems (Crop rotation, Intercropping, Agroforestry), Mulching, Fallowing, Contour Ploughing, Integrated Pest Management (IPM), and Organic Farming.

Tropical Rainforests (TRFs)

• Distribution: Between $10^{\circ}N$ and $10^{\circ}S$. Large basins: Amazon, Congo, SE Asia.
• Characteristics: High temp ($> 26^{\circ}C$), high rainfall ($> 2000\,mm$). Stratification ($5$ layers: Emergent, Canopy, Understorey, Shrub, Undergrowth). Broad leaves with drip-tips and buttress roots.
• Nutrient Cycling: Biomass is the largest store. Rapid cycling. Soil (Oxisol) is infertile due to intense leaching.
• Deforestation Impacts: Global warming (loss of carbon sink), high flood risk, soil erosion, biodiversity reduction, simplified food webs.
• Conservation: National parks (Kinabalu Park), REDD+ ("Money for trees"), Selective Logging, Agroforestry (Inga alley cropping), Eco-product certification (FSC).

Climate Change and Evidence

• Evidence: 2024 was warmest on record ($+1.55^{\circ}C$ above pre-industrial). Sea level rise ($3.7\,mm/yr$ 2006-2018). Thermal expansion and land-ice melting.
• Greenhouse Gases (GHGs): CO2 (Principal knob), Methane (28x potency of CO2), Nitrous Oxide (296x potency). Natural sinks: Forests, oceans.
• Mechanism: Solar short-wave entering, surface absorbing, terrestrial long-wave radiation being trapped by GHGs.
• Impacts: Climate refugees (Tuvalu, Maldives), Coral bleaching, more intense tropical cyclones (Latent heat release), food insecurity.
• Hong Kong Microclimate: Urban Heat Island (UHI). Higher night temps, lower relative humidity, higher cloud cover/particulates acting as condensation nuclei.
• International Cooperation: Kyoto Protocol (Top-down, emission trading), Paris Agreement (Bottom-up, NDCs, goal to limit rise to $1.5^{\circ}C$).

Dynamic Earth: Geology of Hong Kong

• Rock Composition: $85\%$ Igneous ($50\%$ Volcanic/Tuff, $35\%$ Plutonic/Granite), $13\%$ Sedimentary.
• Tuff (凝灰岰): Fine-grained, hexagonal columnar joints (High Island supervolcano), highly resistant, forms high hills (Tai Mo Shan $957\,m$).
• Granite (花崗岰): Coarse-grained, Quartz/Mica/Feldspar, well-jointed, less resistant to chemical weathering. Forms rounded peaks (Lion Rock $495\,m$), badlands (Castle Peak hinterland), and tors (Amah Rock).
• Sedimentary: Clastic rocks (Conglomerate - Pat Sin Leng; Siltstone - Tung Ping Chau). Forms layers/stratification.
• Weathering in HK: Dominant process is Chemical/Spheroidal Weathering due to hot/wet climate. Feldspar turns to kaolin; Mica turns to iron oxide (rusty color).
• Geological Resources: Rock fill, Marine sand fill, Public fill (recycled waste used for projects like HK Port/Airport reclamation). Rock caverns (Shatin Sewage Treatment relocation).