Did you know that our planet has a dynamic surface that is in an ever changing state? Geology isn't just the study of rocks – it's a branch of natural science that focuses on the Earth's physical structure and its history. This includes volcanic eruptions, earthquakes, erosion and weathering, mineral depositions … and the geological processes behind them all.
Geological Processes: Definition
What are geological processes?
Geological processes are the natural forces that shape the physical planet.
Such processes often occur at enormous scales – spanning millions of centuries and thousands of kilometres. A human lifetime is barely a blip on the geological timescale.
The Geological Timescale
The geological timescale (GTS) is a 'calendar' of all of Earth's history, descending chronologically from modern day to the formation of earth. The GTS subdivides all time into abstract units, which are (in descending order of duration): eons, eras, periods, epochs, and ages.
Currently, Earth is in:
- The Phanerozoic Eon
- The Cenozoic Era
- The Quaternary Period
- The Anthropocene Epoch
Examples of Geological Processes
We've learned that geological processes shape our planet. What kind of processes are there?
Mantle Convection
To understand mantle convection, you need to know about the crust and the mantle.
The crust is the thin outer layer of Earth, made up of solid rock and minerals.
The crust is broken up into tectonic plates.
The mantle is Earth's second layer, made up of semi-molten or solid silicate rock.
The mantle is heated by the core below it. As it is heated, its density decreases, so it rises towards the crust. But once the mantle has risen, it begins to cool back down and sink, dragging the crust's tectonic plates above it. This circular movement is known as a convection current.
Nonetheless, not all geological hazards are caused by movement of the Earth's interior. Erosion, weathering, and deposition take place on Earth's exterior, driven by biological, hydrological and atmospheric processes.
You may have heard of tectonic plates in the context of them causing Earthquakes. Earthquakes are caused by the movement of tectonic plates and this can have catastrophic effects on buildings, infrastructure and peoples livelihoods.
Erosion
Erosion is the breakdown and transport of rock particles.
There are six causes of erosion:
Gravity - Bits of land that have been weathered are caused to go from higher to lower ground by gravity eg. Landslides
Wind - Wind erodes rock and carries away the sand created. This further erodes other pieces of land. eg. Brimham Rocks, North Yorkshire.
Rain - Rain-splash erosion causes weathered material such as pebbles or soil to become dislodged. Heavy rainfall then carries sediment into streams and rivers. eg. Rain gullies in Black Ven landslide, Lyme Regis, Dorset.
Glaciers - These are massive rivers of ice heavy ice that flow slowly and erode away big portions of land, depositing the debris at their tip eg. An Teallach, in Ross and Cromarty
Oceans - Both current and rising and falling tides cause erosion of coastal areas. eg. Newbiggin Cliff near Filey, North Yorkshire
River - Rivers both erode and build up land. Meanders form when fast flowing water on an outside curve flows faster than water on the inside. The water on the outside has more power to erode and extend that riverbank while slower water on the inside curve deposits material carried by the river on the inside riverbank. eg. the River Forth
Weathering
Weathering is the breakdown of rocks while they remain in their place.
Causes of weathering can be biological, chemical, or physical.
Biological: plants grow in a crack in a rock, causing the crack to widen as the roots increase in size.
Chemical: acidic rainwater reacts with compounds in the rocks, causing them to break down.
Physical: water in a crack freezes and expands, causing the crack to expand over time.
Erosion and weathering are often confused; they're similar processes. However, erosion involves MOVEMENT, whilst weathering does not.
Deposition
Deposition is the laying down of sediment.
Sediment can be transported as various sizes (pebbles, sand, silt, or dissolved in water) by:
How Can Geological Processes Cause Hazards?
Firstly, what is a hazard?
A hazard is something that has the potential to cause harm to life and human property.
A hazard can result in disaster if it causes damage and destruction.
Hazards at Plate Boundaries
Hazards are common at the boundaries between tectonic plates due to the build up and release of pressure.
Earthquakes: an earthquake is a sudden violent shaking of the Earth's surface. Severe earthquakes can cause widespread damage and destruction, sometimes taking thousands of lives.
Tsunamis: these enormous waves are caused by the displacement of a large volume of water. Marine earthquakes or undersea volcanic eruptions have the potential to generate a tsunami.
Volcanoes: a volcano is a rupture in Earth's crust, from which lava, ash, and gas can escape.
There are two kinds of volcano: shield and composite.
Composite volcanoes are the stereotypical, steep-sided volcanoes. They emit viscous acidic lava during infrequent yet violent eruptions.
Mount Vesuvius, the infamous destroyer of Pompeii, is a composite volcano.
Shield volcanoes are gently sloping volcanoes that emit basic, runny lava. The eruptions are more frequent but less violent.
Eyjafjallajökull, an Icelandic volcano, erupted multiple times in the spring of 2010. No one was killed, but the ash cloud produced disrupted flights for several months.
Hazards at Coastal Zones
Geological processes such as erosion and weathering are common along the coastline, where the constant movement of water and wind breaks down rocks. This breakdown can lead to sudden mass movement of rock, which has the potential to cause harm.
Rockfall: rock suddenly breaks away from a steep cliff, triggered by weathering, and forms down the slope to form scree.
Mudflows: earth and mud flow downhill over unconsolidated rock. If it's sudden and fast-flowing, it can present a hazard.
Landslide: rock moves rapidly downhill, often mixed in with mud. Landslides are triggered by very heavy rainfall and can cause a threat to people.
In June 1993, a major landslide destroyed the Holbeck Hall Hotel in Scarborough, North Yorkshire. Over two days, a rotational landslide cut away 70 metres of the cliff. The area had experienced heavy rainfall in the prior months. Poor drainage led to a build up of water pressure.
What are the Effects of Geological Processes?
Over time, geological processes can create landforms. These features on the Earth's surface make up the terrain.
Features on land include mountains, plains, and valleys.
Coastal features include bays, spits, and peninsulas.
Underwater features include mid-ocean ridges, trenches, and ocean basins.
There are two different ways of organising landforms.
They can be categorised by their physical attributes:
Slope
Soil type
Elevation
Rock exposure
Orientation (direction)
Or by the geological processes that created them:
Wind
Erosion
Weathering
Glacial movement
Tectonic plate movement
Deposition
The Himalayas were formed by the collision of the Eurasian and Indian tectonic plates. Unsplash
What is the Importance of Geological Processes?
Geological processes don't just affect rocks and create landforms; they are tightly linked to life and biodiversity. For example, substrate composition plays an important role in determining biodiversity. The underlying rock type influences the species of plants that grow in an area; in turn, this affects the community composition. The properties of underlying rock can also determine drainage and water availability.
As well as impacting biodiversity, geological processes create resources used by humans in their day-to-day lives.
Energy Resources
Most of the world's electricity is generated by burning fossil fuels – the remains of organisms from millions of years ago. Geological processes such as heating, pressure and sedimentation convert the remains into energy-dense fuels.
Coal, a fossil fuel, is formed by geological processes acting on ancient plant remains. Unsplash
Peat bogs are another source of energy. These bogs are dense wetlands filled with partially decayed vegetation. In some parts of the world, such as Ireland, peat bogs are a major energy resource and are burned to heat houses.
Food and Drink
Soil properties and mineral composition influence the plants that can grow in that area.
Potatoes grow best in highly acidic (pH 5 to 6.5), well-drained, sandy soils.
Drinking water (as well as water for domestic use) originates from sources above and below ground. The sources underground are known as aquifers – water stored in rock layers.
Minerals
Geological processes result in mineral deposits. Some can be useful for humans.
Fluoride is a naturally occurring mineral added to toothpaste to protect teeth from developing cavities.
Calcium is a mineral required for healthy bones and teeth, found in dairy products. Originally, calcium is found in the soil and taken up by grass, which is eaten by cows. Over time, calcium builds up in their bodies and milk.
Minerals such as gold, cobalt, and lithium are used to build computers and smartphones.
I hope that this article has explained geological processes for you. These natural forces shape our planet, creating landforms and useful resources, but these powerful processes can cause hazards that risk human lives.
Geological Processes - Key takeaways
- Geological processes are the natural forces that shape the physical planet. These processes occur at massive scales - over millions of years and thousands of kilometres.
- Geological processes include convection currents in the mantle, erosion, weathering, and deposition.
- Geological processes can cause hazards. At plate boundaries, hazards such as earthquakes, tsunamis, and volcanoes are common. Coastal zones experience hazards like rockfall, mudflows, and landslides.
- Geological processes create landforms. These are classified according to their formation or physical properties.
- Biodiversity and natural resources are closely linked to geological processes.
1. British Geological Society, Holbeck Hall, Scarborough, 2022
2. International Commission on Stratigraphy, Geologic time scale, 2022
3. Magnús T. Gudmundsson, Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland, Nature, 2012
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