Understanding Seismic, Volcanic Hazards & Land Relief

Posted on Feb 27, 2025 in Geology

Internal Activity Hazards

Seismic Hazard

Earthquakes mainly develop at plate boundaries.

Constructive and passive boundaries are usually under sea level, thus they have a minimum seismic hazard degree. However, they may produce tidal waves (tsunamis).

Destructive boundaries develop many powerful earthquakes, and this often occurs in highly populated areas. That’s why these zones have the highest seismic hazard (fire belt).

Volcanic Hazard

The volcanic hazard depends on the magma viscosity (which, in turn, depends on the amount of silica) and on the gas content.

Volcanic activity in hot spots and constructive boundaries is produced by magma coming from the mantle, with a poor-silica composition. These volcanoes emit very fluid lavas.

Volcanic activity in destructive boundaries (subduction zones) is produced by partial melting of crustal rocks, with a high content of water (wet sea floor rocks) and silica. These volcanoes produce explosive eruptions (fire belt).

Seismic and Volcanic Hazards in Spain

The Iberian Peninsula is located next to the Europe-Africa boundary, although the area is not very active.

Seismic hazard is related to young mountain ranges. The maximum seismic hazard level is located in Andalusia, in the internal zones of the Beticas mountain range.

Volcanic hazard is only present in the Canary Islands. There are no active volcanoes in the Iberian Peninsula. The most recent volcanic activity, which ended a few million years ago, is located in Olot (Girona), Gata Cape (Almeria) and Calatrava (Ciudad Real).

Land Relief

Land relief is the entirety of geographical elements that make up the Earth’s surface. Internal processes tend to create new land masses (volcanism, mountain building (orogenesis)), whereas external processes tend to carve it.

Factors Controlling the Morphology of Landforms

• Climate: It is the most important factor: it controls the acting geological agents in each place, and the type of vegetation that covers it.
• Rock composition: The same geological agent produces different landforms over different rocks with different physical properties.
• Structure: The geometry of rock layers may control the land relief if there are different rocks with different physical properties.
• Geological history: Since geological agents act throughout time, different stages of development can be seen.
• Human activity: Human activity can change land relief directly (cities, tunnels, roads) or indirectly (global warming).