Geological Hazards, Risks and Natural Resources; Geological Maps and Cross-Sections
Domain 5 combines hazard science with map interpretation. The exam expects a precise definition chain - hazard, exposure, vulnerability, risk - applied to Canarian volcanoes, seismicity and landslides, plus the ability to read a geological map and construct or correct a cross-section.
Hazard, risk and the probability chain
Hazard = probability of a damaging natural event of given magnitude in a time window. Exposure = people, assets and infrastructure in the affected area. Vulnerability = the degree of damage suffered by what is exposed. Risk ≈ hazard × exposure × vulnerability, modulated by resilience and land-use planning. Mitigation: monitoring, hazard maps, building codes, evacuation plans, insurance, education. Prediction (when) differs from forecast (probability) and from prevention (impossible for volcanic eruptions, possible for some landslides and coastal erosion).
Canarian hazards
Volcanic: lava flows (Tajogaite, 2021, La Palma), pyroclastic fall and surges, ash damaging crops and aviation, volcanic gases (CO₂ in depressions), lahars on steep slopes, tsunamis from flank collapse. Seismic: moderate, volcano-tectonic swarms, Enmedio submarine volcano. Mass movements: Guimar and Orotava mega-landslides, rockfalls in barrancos. Coastal: storm overwash and erosion. Wildfire in pine forest is an environmental hazard closely tied to drought.
Natural resources
Groundwater (galerías, pozos, nacientes), geothermal energy (Teide, Gran Canaria), volcanic aggregates and pozzolana, fertile volcanic soils (jable, picón), salt, tourism linked to geodiversity, and geosites (UNESCO Global Geopark of El Hierro).
Maps and cross-sections
Contour lines give relief; spacing indicates slope. Geological boundaries follow topography unless vertical. Strike and dip symbols: dip is perpendicular to strike, measured from horizontal; a vertical bed has 90° dip and no trend. V-rule: boundaries point upstream in valleys unless vertical. In a cross-section, maintain vertical exaggeration consistently, extend boundaries to depth with realistic dip, and show a fault cutting the youngest bed it displaces.
Worked example
A map shows horizontal strata cut by a vertical fault with 200 m downthrow, overlain unconformably by flat-lying basalt flows. Task: draw the cross-section. Reasoning: horizontal strata stay horizontal across the section; the fault offsets them vertically and must be drawn as a steep line cutting them; the basalt flows were erupted after faulting, so they cover the fault with no offset. That single observation fixes the relative chronology: strata → faulting → erosion → basalt eruption.
Traps that cost marks
Defining risk as equal to hazard. Calling an eruption preventable. Drawing a fault that offsets the youngest unit. Contradicting map dip values in the section.
- Risk needs hazard, exposure and vulnerability together.
- A vertical bed has no strike trend and 90° dip.
- Downthrown side is on the side of the fault symbol's tick marks.
- The youngest unit is what the fault does not cut.