6.2: Forces that Shape the Surface of the Earth

Endogenic Processes and the Lithosphere 

The lithosphere is constantly being altered by these forces originating from within and outside the Earth system. Great forces from within causes the surface to heave and buckle, sometimes with disastrous consequences to humans. Energy received from the sun drives processes like those that create majestic sand dunes and carve magnificent stream valleys.

Driven by the Earth’s internal heat engine, endogenic processes reshape our planet from the inside out. This geological activity begins deep in the core, where the radioactive decay of elements like uranium, thorium, and potassium generates immense heat. This energy rises into the mantle, fueling convection currents that act as a slow-moving conveyor belt, tugging on the lithospheric plates above illustrated in Figure \(\PageIndex{1}\).

Figure \(\PageIndex{1}\): Cross-section of Earth showing circular mantle convection currents driving the horizontal movement of tectonic plates. (CC BY 4.0; Paul Webb via Introduction to Oceanography).

Figure \(\PageIndex{1}\) is a cross‑section diagram of Earth showing internal layers and mantle convection currents that drive plate motion.

Surface and lithosphere:

• At the top, a thin rigid layer represents the lithosphere, which includes tectonic plates.
• Small horizontal arrows along this layer indicate that the plates are moving apart at the center and toward each other at the edges.

Asthenosphere and mantle:

• Just below the surface is the asthenosphere, a softer, flowing layer of the upper mantle.
• Below this is the broader mantle, labeled and extending down to approximately 700 km depth in the upper region of the diagram.

Convection currents:

• Curved arrows within the mantle form large loops, representing convection currents:
  • Upward arrows show hot material rising from deeper in the mantle.
  • At the top, this rising material spreads outward beneath the lithosphere.
  • Downward arrows show cooler material sinking back toward deeper layers.
• These circular motions form continuous convection cells.

Core:

• The outer core is shown as a large layer below the mantle.
• The inner core is shown as a smaller central circle.
• These layers indicate the source of internal heat that drives convection.

Relationships and movement:

• Where mantle material rises, the surface plates move apart.
• Where mantle material sinks, plates move toward each other.
• The movement of plates is linked directly to the convection currents below.

Function:

The diagram illustrates how heat from Earth’s interior drives mantle convection, which in turn causes plate tectonic motion:

• Rising hot material pushes plates apart.
• Sinking cooler material pulls plates downward.

This process explains major geologic activity such as seafloor spreading, mountain building, and subduction.

As these plates are moved, they interact by colliding, diverging, or sliding past one another. These interactions are the primary architects of Earth's landscape; they trigger earthquakes, spark volcanic activity, and forge massive geographical features. From the towering heights of the Himalayas formed by plate collisions to the profound depths of the Marianas Trench caused by oceanic plate interaction, the Earth’s surface is a direct reflection of the powerful thermal energy churning beneath it. 

Figure \(\PageIndex{2a}\): Mt. Shishaldin, Alaska is a composite volcano. (CC BY-SA 4.0; Michael E. Ritter via  The Physical Environment).

Figure \(\PageIndex{2a}\) depicts Mt. Shishaldin, Alaska which is a nearly symmetrical, snow-covered composite volcano. It serves as a visual example of how endogenic forces move magma to the surface, creating new landforms. The peak illustrates the result of repeated eruptions of lava and pyroclastic material, a direct consequence of plate tectonics and internal thermal energy.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure \(\PageIndex{2b}\): Teton Mountains were created by faulting. (CC BY-SA 4.0; Michael E. Ritter via  The Physical Environment).

Figure \(\PageIndex{2b}\) shows the dramatic vertical relief of the Teton Range. These mountains were formed through faulting—a process where the Earth's crust is broken and displaced. This highlights how internal tectonic stresses can heave and buckle the surface to create massive mountain systems. 

Exogenic Processes and the Lithosphere

Exogenic processes are those that shape the Earth's surface through forces primarily driven by solar energy. These processes include wind erosion, which occurs when unequal solar heating creates pressure gradients that set air in motion, allowing the wind to detach and transport soil. Similarly, water erosion is fueled by the sun’s energy through the hydrologic cycle, where solar-driven evaporation eventually leads to the precipitation that carves the landscape. Glacial activity is also a key exogenic force; when solar intensity is low enough that winter snow persists through the summer, it accumulates and metamorphoses into massive ice sheets that sculpt the terrain as they move.

Figure \(\PageIndex{3a}\): Water Erosion. Severe sheet erosion on farm land. (CC BY-SA 4.0; Michael E. Ritter via  The Physical Environment).

 

 

 

 

Figure \(\PageIndex{3a}\) shows a farmland landscape scarred by severe sheet erosion. It demonstrates the power of running water (initially evaporated by solar energy and returned as rain) to detach and transport soil particles, physically stripping the topsoil from the land. 

 

Figure \(\PageIndex{3b}\): Wind Erosion. Massive dust storm during the Dust Bowl era. (CC BY-SA 4.0; Michael E. Ritter via  The Physical Environment). 

This historical photograph (Figure \(\PageIndex{3b}\)) from the Dust Bowl era shows a massive, dark wall of dust approaching a settlement. It illustrates the role of wind—created by pressure gradients and unequal solar heating—as a powerful exogenic agent capable of transporting vast amounts of sediment across the surface.

Figure \(\PageIndex{3c}\): Glacial Erosion. Alpine glaciers are found on all continents today at high altitudes. (CC BY-SA 4.0; Michael E. Ritter via  The Physical Environment).

Figure \(\PageIndex{3c}\) shows an alpine glacier nestled between high mountain peaks. It represents the geological work of ice. When solar energy is insufficient to melt winter snow, it accumulates and metamorphoses into glacial ice, which then flows under its own weight to sculpt and carve the mountain valleys below.