Landscapes: Tectonic Activity and Erosion

Processes That Transform Landscapes

• Earth's crust comprises several plates sitting on semi-molten material in the mantle.
• Convection currents, powered by the Earth's core heat, move these plates.
• Plate movement causes most of Earth's mountain formation.
• Tectonic activity (or force) refers to the forces caused by these movements within the Earth's crust.
• Erosion and deposition commonly change or create landscapes.
• Water breaks up, moves, and repositions landscape material.
• Torrents of water can move rocks and shape valleys.
• Gentle rain alters the chemical structure of surface material, promoting soil transport.
• Glaciers act as slow-moving bulldozers in cold climates, eroding land.
• Ocean waves shape coastal landscapes.
• The Colorado River formed the Grand Canyon by cutting deep channels into rock.

Erosion

• Erosion is the wearing away of the Earth’s surface by natural elements (wind, water, ice) and human activities.
• Eroded materials can be transported to new locations by wind, water, and ice, further eroding the existing landscape.
• Deposition of transported material can create new landforms.
• Human activities increase erosion, sometimes by up to 40%.
• Deforestation, agriculture, urban sprawl, logging, and road construction disrupt the natural balance.
• Vegetation binds the soil, so its removal increases erosion.

Deposition

• Deposition occurs when materials are transported by rivers, wind, ice, or ocean currents.
• Deposition involves moving materials like rock, soil, and sand to new locations.
• Human activities affect the deposition process.
• Dam construction causes material to build up behind dam walls.

Change Over Time

• Water changes the shape and size of landforms and features.
• Coastal landscapes evolve over long periods, such as the changing formations of the Twelve Apostles.

Moving Water

• Erosion, transportation, and deposition by running water shape landscapes.
• Rivers are either perennial like the Gordon River in Tasmania or intermittent like Coopers Creek in QLD.
• The Colorado River in the USA has eroded incredible landforms like the Grand Canyon.
• The water cycle (evaporation, rain, flow, groundwater) demonstrates constant movement and change.

River Systems and Features

• Rivers are natural features linked to different parts of the Earth.
• Lithosphere (rocks and soil)
• Hydrosphere (water)
• Biosphere (plants and animals)
• Atmosphere (temperature and water cycle)
• Changes can occur quickly or slowly where a change at one location can affect other locations along the same river.
• Water flows downhill, starting at a higher altitude source and ending at the lower altitude mouth.
• Rivers erode, transport, and deposit material, depending on the water volume and flow speed.
• Fast-flowing, flooded rivers erode and transport significant material downstream.
• Decreasing speed or volume results in material deposition.

Watershed

• Rivers gather water from a drainage basin/catchment.
• Watersheds (mountain or hilltops) define drainage basin boundaries.

River Formation

• Large rivers originate from rain or melting snow in mountains or hills.
• Water collects in rills.
• Rills combine to form streams.
• Streams join to create a river.

Upper Course

• Water flows over steeper slopes, cutting downwards to create V-shaped valleys.
• Rivers tend to follow a straight course in the upper reaches.

Waterfall

• Waterfalls form when a river encounters resistant (hard) rock.
• Rapids form when a river crosses bands of resistant rock.
• Turbulent water flow in rapids creates "white water."
• Plunge pools form at the base of waterfalls due to erosion from fast-flowing water.

Meanders

• Rivers widen on flatter land due to increased water volume from tributaries.
• Erosion occurs mostly sideways, widening the river valley.
• Sideways erosion forms meanders (curves).
• Meandering rivers change course over time.
• Cut-off meanders create oxbow lakes.

Tributary

• Tributaries are rivers or streams that add water to the main river.
• Confluence describes the place where two rivers join.

Floodplains

• Floodplains are created by flooding over thousands of years.
• Flooding rivers deposit alluvium (fertile sediment) outside the riverbanks.
• Floodplains are suitable for farming and settlement.

River Mouth

• Deltas form at the mouths of large rivers where sediment is deposited faster than the sea can remove it of mud, sand, and clay.
• Rivers split into distributaries to navigate through deposited material.
• Delta shapes include fan, arrow and bird-foot.
• Delta shape is influenced by tides, ocean waves, sediment volume, and river water.
• Estuaries are wide river mouths where fresh and salt water mix.

Constructive Waves

• Smaller waves carrying less energy are known as constructive waves.
• Constructive waves deposit sand and shells on the beach, building new coastal features.
• Beaches are depositional coastal landforms.
• Constructive waves reposition materials to create spits, sand dunes, and lagoons.
• Material (sand, shells, coral, pebbles) comes from eroding cliffs, offshore sources, or rivers.

Erosion of Coastal Landscapes

• Coasts are the border between land and ocean.
• Seawater movement and ocean impact create coastal landscapes.
• Coastal landforms are similar worldwide due to similar formation processes.
• Wave action and rainfall attack cliffs eroding weak points.
• Water runoff carries eroded material into the sea.
• Waves undercut cliffs to form notches.
• Growing notches cause unstable sections to fall into the sea.
• Swash is the wave washing onto the beach.
• Backwash is the wave returning down the beach into the sea.
• Powerful backwash from destructive waves removes beach sand offshore.
• Destructive waves possess a power ocean swell that can create good surf, but unsuitable waters for swimming.
• Tectonic forces, sea levels, and human activities also affect coastal landscapes.

Coastal Landscape Features Created By Erosion

• Cliffs, headlands, bays, caves, and stacks are landforms found along eroding coastlines.
• Destructive waves remove sand from beaches, destroy vegetation on dunes, and damage protective management features.

Constructive Waves

• The wind shapes construction material brought onshore by wave swash.
• Wind dries material, blowing it inland to create dunes.
• Wind influences the angle of waves approaching the coast.
• Waves move towards the shore at an angle, so swash pushes material onto the beach at an angle.
• Backwash returns to the sea via the shortest route.
• Longshore drift is the zigzag movement of material along the beach, following the prevailing wind direction.
• Longshore drift creates spits and bars.
• Changes in prevailing wind direction alter longshore drift direction.

Karst Landscapes

• Karst is a network of underground caves and channels carved by rivers and streams.
• Water dissolves bedrock over long periods.
• Sinkholes, vertical shafts, and fissures are visible on the surface.
• Intricate drainage networks occur underground, including caves, rivers, stalactites, and stalagmites.
• Karst topography makes up about 10% of the Earth’s surface.
• One-quarter of the world’s population depends on karst environments for water.

Karst Landscape Formation

• Water becomes acidic by mixing with carbon dioxide in the atmosphere.
• Acidic water dissolves soluble bedrock (limestone and dolomite).
• This creates cracks (fissures), allowing water to move through the rocks.
• Lateral erosion occurs when water reaches non-dissolving rock layers, forming underground rivers or streams.
• Water creates hollows and caves.
• Some karst landscapes contain aquifers for water storage.

Location of Karst Landscapes

• Karst landscapes are found worldwide.
• Tropical regions can develop karst mountains due to rainfall.
• Australia's Nullarbor Plain contains the Earth’s largest arid limestone karst cave system.
• Fossils in these caves relate to a distant past and significant Indigenous cultural sites.

Landscapes In The Pacific Region

• The Pacific Ocean is the world’s largest, covering almost 1/3 of the Earth’s surface.
• It stretches from the Arctic to the Antarctic, and from Australia/Asia to the Americas.
• There are 25,000 Pacific Islands with a population of about 10 million.

Water In Australia

• Australia has a small area of permanent rivers and streams.
• Australia is the driest inhabited continent:
  • Least run-off
  • Lowest percentage of rainfall as run-off
  • Least amount of water in rivers
  • Smallest area of permanent wetlands
  • Most variable rainfall and stream flow
• Australian lakes hold little water compared to other continents.
• Largest lakes, Kati Thanda-Lake Eyre and Lake Torrens, become salt and mud beds during dry seasons.
• South Australia is the driest state with few permanent rivers and streams.

Landscapes and Landforms

• Landscapes are visible features across an area, that are created by environmental processes and human activity.
• Examples include mountains, coasts, and deserts.
• Landforms are distinct natural features like hills, canyons, dunes, and valleys.

Processes That Shaped Australia's Landscapes and Landforms

• Tectonic forces and surface forces (weathering, erosion, deposition) have created Australia's major landforms.
• Geomorphic processes include weathering, erosion, and deposition.
• Mountain ranges have eroded, causing thick sediment to cover land areas.
• Sediment formed sedimentary rocks prone to folding, faulting, and uplifting.
• The Earth's crust buckled and folded along fault lines (weak points), causing uplift.
• Weathering and erosion have worn these features down over time.
• Erosion on softer rocks forms valleys and bays.
• Harder rocks remained as mountains, hills, and headlands.

Key Terms

• Tectonic
• Weathering
• Erosion
• Deposition
• Geomorphic
• Fault line

Global Landscapes

• Variations in landscapes are influenced by climate, geographical features, latitude, human impact, and location.

Mountain Landscapes

• Mountains rise above surrounding land, with steep sides and high peaks, some with snow-covered peaks.

Desert Landscapes

• Deserts are arid environments with low rainfall and temperature extremes.
• Not all deserts are hot; Antarctica is the world’s largest desert.

Rainforest Landscapes

• Rainforests are the most diverse landscapes, ranging from hot, wet tropics to cooler, temperate areas.
• They rely on high rainfall and have lush vegetation.
• Over 50% of all known plant and animal species are found in rainforests.

Grassland Landscapes

• Grasslands/savannas are transitional landscapes between forests and deserts.
• They contain grasses and small or widely spaced trees, often inhabited by grazing animals.

Polar Landscapes

• Polar regions and tundra are found in polar and alpine locations, characterized by permafrost.
• Vegetation includes dwarf shrubs, grasses, and lichens adapted to extreme cold and short growing seasons.
• Glaciers shape landscape features.

Karst Landscapes

• Karst landscapes form when water containing chemicals flows over soluble rock like limestone, causing fractures and underground drainage systems.
• Aquifers that can provide water
• eg. Limestone pavements, disappearing rivers, reappearing springs, sinkholes, caves, karst mountains.

Aquatic Landscapes

• Aquatic landscapes cover three-quarters of the Earth, classified as freshwater or marine.
• Marine regions include oceans and coral reefs (saltwater).
• Freshwater regions include lakes, rivers, estuaries, and wetlands.

Island Landscapes

• Islands are land areas completely surrounded by water (continental or oceanic).
• Continental islands lie on a continental shelf.
• Oceanic islands rise from the ocean floor and are volcanic.
• An archipelago is a group or chain of islands.

Built Landscapes

• Built landscapes are created or altered by humans.