Dynamic Earth: Natural Processes and Environmental Risks

Equilibria on a Dynamic Planet

The Sun heats the Earth's surface, which in turn warms the surrounding air. Simultaneously, the core heats the planet's interior. This leads to unequal heating density, causing less dense materials to rise. The familiar water cycle—rain, runoff, infiltration, and evaporation—is driven by solar energy, but it does not act alone. Another hydraulic system, hidden from view, distributes heat across the seas through a cycle of ocean currents known as the ocean conveyor belt. The movement of mantle material causes deep-seated activity that feeds volcanoes, expelling gases such as carbon, nitrogen, and sulfur. This creates a highly dynamic system with many delicate balances, as the Earth's temperature is constantly changing.

Hostile Environmental Risks

Humans arose in a changing and unpredictable world. As we inhabited the Earth, we learned to recognize and avoid dangerous locations, such as areas prone to volcanoes and earthquakes. However, as the human population increased dramatically, people began to build homes in increasingly unsafe areas, thereby escalating risk.

Dangers of Heavy Rainfall

Floods remain the natural phenomenon that causes the most casualties. Floods are the overflow of rivers or streams, which are intermittent watercourses. In the Mediterranean area, these are called wadis. They occur when intense rainfall exceeds the capacity of channels to evacuate the water. Heavy rains also exacerbate environmental problems like erosion, while landslides involve the falling of materials down steep slopes.

Earthquakes, Tsunamis, and Volcanoes

Earthquakes occur when the ground vibrates, potentially causing buildings to collapse. The mobility of lithospheric plates generates high-energy earthquakes, particularly at the edges of constructive plates.

Tsunamis are giant waves caused by sudden deformations of the seabed. These can be triggered by:

• Earthquakes affecting the seafloor
• Tidal waves
• Explosions of volcanic islands
• Submarine landslides

Their wavelength spans kilometers; when they reach the coast, water accumulates, reaching heights of 10 to 15 meters and penetrating several miles inland.

Volcanic eruptions have caused approximately 300,000 deaths in the last 400 years. While lava emission is dangerous, viscous magmas can clog a volcano's chimney. This creates a pressure cooker effect; when the pressure exceeds the strength of the chimney, the volcano bursts, launching magma particles at high speeds within clouds of hot gas (pyroclastic flows). If these clouds fall into a riverbed, they become hot mudflows.