Tierra 3

5. Internal activity hazard
5.1. Seismic hazard
Earthquakes develop mainly in plate boundaries
Constructive and passive boundaries are usually under the sea
level, thus they have a minimum seismic hazard degree. However,
they may produce tidal waves (tsunamis).
Destructive boundaries develop many powerful earthquakes, and at
the same time, it occurs in usually highly populated areas. Thats
why that zones have the highest seismic hazard (fire belt)
5.2. Volcanic hazard
The volcanic hazard depends on the magma viscosity (which, in turn,
depends on the amount of silica) and on the gas content.
The 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.
The 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)
5.3. 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 placed 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).
6. Land relief
Land relief is the whole of geographical elements that make up the Earths
surface. Internal processes tend to create new land masses (volcanism, mountain
building (orogenesis)…, whereas external processes tend to carve it.
6.1. 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 bee seen.
Human activity: Human activity can change land relief directly (cities,
tunnels, roads…) or indirectly (global warming)

Morphoclimatic system	Climate	Geological agent	Landforms
Glacial	Average annual temperature below 0ºC so that winter snow doesn't melt during summer	ice currents (glaciers)	horns, U-shaped valley, cirques, moraines
Periglacial	average annual temperature equal to 0ºC so that most days water freezes and thaws	freeze and thaw (gelifraction, cryoturbation)	frost-scattered bedrock, (blockfields or felsenmeer), earth hummocks, ice-wedge polygons, stone circles
Wet temperate	wet, temperate climate. rainfalls are typically drizzles	fluvial action	fluvial landforms: V-shaped valleys, meanders, flooding plains
Arid (desert)	very dry climate with high daily temperature oscillations	wind, heat (thermoclasty)	rocky desert, stony fields, (reg), dune masses (erg)
Semi-arid	dry climate. rainfalls are typically strormy	water runoff	wadies, badlands, fairy chimneys
Tropical	warm, humid climate	chemical weathering	plains, inselbergs