Landscape Systems: Endogenic vs Exogenic Energies

Landscape systems are the sets of interacting processes that build up and wear down the land surface, and they are driven by two kinds of energy: endogenic (internal) energy from Earth’s interior, which creates relief through plate tectonics, volcanism and uplift, and exogenic (external) energy from the Sun and gravity, which wears relief down through weathering, erosion and deposition. In brief: mountains rise when endogenic processes lift rock and are lowered when exogenic processes remove it. A landscape is an open system: energy and sediment enter and leave, and the shape of the land reflects the balance between the two. When uplift and erosion are in balance, a landscape can stay in dynamic equilibrium, with a stable form despite constant change.

Understanding both sets of forces explains why mountain ranges look as they do and how fast the land changes. This guide explains endogenic and exogenic energy, the systems approach, how uplift and erosion interact, compares the two energy types in a table, works through calculations, outlines the history of ideas and corrects common mistakes.

What is endogenic energy?

Endogenic energy comes from within the Earth, mostly from heat left over from the planet’s formation and from the radioactive decay of elements such as uranium, thorium and potassium in the mantle and crust. This heat drives convection in the mantle, which moves plates and powers tectonic uplift and subsidence, folding and faulting, earthquakes, volcanism and the creation of ocean basins. These processes are constructive: they create relief, such as mountain ranges, rift valleys, volcanoes and ocean trenches, and provide the “raw material” for exogenic processes to work on. Uplift rates are usually a fraction of a millimeter to a few millimeters a year, but can reach around 10 mm per year in the fastest-rising regions, such as the Nanga Parbat massif in the Himalaya.

What is exogenic energy?

Exogenic energy comes from outside the solid Earth, chiefly from solar radiation, which drives the weather, climate and the water cycle, and from gravity, which pulls water, ice, rock and soil downhill. The processes it powers are weathering, erosion, transport and deposition by rivers, glaciers, waves, wind and mass movement. They are mostly destructive in uplands, since they lower and smooth the surface, and constructive in lowlands, where they deposit sediment to build floodplains, deltas, beaches and dunes. Climate controls the rates and kinds of process: glaciers dominate cold regions, rivers and chemical weathering are strong in humid areas, and wind in deserts. Biological activity and human actions, such as farming and mining, are further agents that add to the exogenic effects.

How do landscapes behave as systems?

A landscape can be seen as an open system with inputs (solar energy, precipitation, tectonic uplift, sediment from upstream), stores (soil, sediment, ice), flows (the movement of water and debris downslope) and outputs (sediment and solutes carried to the sea). Several ideas from systems thinking are important.

• Feedbacks: negative feedback restores balance, for example, a steeper slope erodes faster, which reduces the slope. Positive feedback amplifies change, such as gullying that concentrates water and deepens the gully.
• Dynamic equilibrium: a landscape can maintain a steady form while energy and material continue to pass through, as when uplift is balanced by erosion. G. K. Gilbert and John Hack developed this idea.
• Thresholds and complex response: a system may suddenly change when a limit is passed, such as a slope failing in a landslide, or a river cutting a new channel.
• Relaxation time: the time needed for a landscape to adjust to a change (such as a change in climate or sea level), which may be thousands to millions of years.
• Scale: processes act at scales from a grain of sand to continents, over seconds to hundreds of millions of years.

How do uplift and erosion interact?

Where uplift is faster than erosion, relief and altitude increase. Where erosion is faster, the land is lowered. Steep slopes erode more quickly, so a rising mountain range reaches a state in which erosion balances uplift. The relationship is complicated by isostasy: the crust floats on the denser mantle, like an iceberg in water, so when erosion removes mass, the crust rebounds upward. Because the crust has a density of about 2.7 g/cm³ and the mantle about 3.3 g/cm³, about 82% (2.7 ÷ 3.3) of the eroded thickness is compensated by rebound, which means that erosion lowers the summits much more slowly than it removes rock. This is why mountain belts can last for hundreds of millions of years. Erosion in turn can influence tectonics, since unloading and the focusing of deformation in valleys can change where rocks are uplifted, an area of current research.

Endogenic and exogenic processes compared

Worked example: rates, balance and isostasy

1. Time to remove a mountain: a range 3,000 m high is eroded at an average of 0.5 mm per year (0.0005 m). The time needed is 3,000 ÷ 0.0005 = 6,000,000 years, ignoring isostatic rebound.

2. Net change in height: if the uplift is 1.0 mm per year and the erosion is 0.8 mm per year, the net rise is 1.0 − 0.8 = 0.2 mm per year, or 200 m in a million years.

3. Dynamic equilibrium: if the erosion rate increases to 1.0 mm per year, the net change is zero, and the mountain height stays constant even though 1 m of rock is removed every 1,000 years.
4. Isostatic compensation: the fraction of eroded thickness that is compensated by rebound is the crust density divided by the mantle density: 2.7 ÷ 3.3 = 0.82. So when 1 m of rock is eroded, the surface falls by 1 − 0.82 = 0.18 m.

5. Eroded thickness needed: to lower the average height by 1,000 m, the thickness that must be eroded is 1,000 ÷ 0.18 = about 5,500 m, which shows why deep roots of ancient mountains are exposed at the surface after long erosion.
6. Sediment output: a basin of 10,000 km² (10¹⁰ m²) lowered at 0.2 mm per year loses 10¹⁰ × 0.0002 = 2,000,000 m³ of rock a year, about 5.4 million tonnes at a density of 2.7 t/m³.

How have ideas about landscape change developed?

James Hutton in the 18th century realized that landscapes are shaped by slow uplift and erosion over vast times. William Morris Davis proposed in 1899 the “cycle of erosion,” with stages of youth, maturity and old age after a rapid uplift, and it dominated geomorphology for decades. Walther Penck (1924) stressed that uplift and erosion happen at the same time, and G. K. Gilbert and John Hack proposed dynamic equilibrium. Plate tectonics, accepted in the 1960s, gave a framework for endogenic forces, and the development of dating methods (cosmogenic nuclides, thermochronology) since the 1980s has allowed rates of uplift and erosion to be measured. Today, researchers use numerical models to explore how tectonics, climate and erosion interact.

Which mistakes are common?

Mistake 1: Thinking that uplift happens first and erosion later

Both operate together, and landforms reflect the balance between them at any time.

Mistake 2: Believing that erosion simply lowers mountains at the rate of removal

Isostatic rebound compensates for most of the lost mass, so the height falls much more slowly than the rock removed.

Mistake 3: Treating endogenic and exogenic processes as independent

Climate and erosion affect tectonics, and uplift changes climate, for example by creating rain shadows and glaciers.

Mistake 4: Assuming that landscape change is always slow and steady

Most change is slow, but landscapes also change in sudden events such as earthquakes, floods and landslides, and past climates and rates can differ from current ones.