How Tectonic Hazards Form
Part of Tectonic Hazards — GCSE Geography
This deep dive covers How Tectonic Hazards Form within Tectonic Hazards for GCSE Geography. Revise Tectonic Hazards in The Challenge of Natural Hazards for GCSE Geography with 14 exam-style questions and 24 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 2 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 2 of 12
Practice
14 questions
Recall
24 flashcards
🔍 How Tectonic Hazards Form
The Earth's outermost layer — the lithosphere — is not a single solid shell. It is broken into roughly 12 large tectonic plates and several smaller ones, all moving slowly across the surface of the planet. This movement is driven by convection currents in the semi-molten mantle below: hot rock rises, spreads outward, cools, and sinks again in a slow churning cycle. The plates move at roughly 5 cm per year — about the speed your fingernails grow. Over millions of years, these tiny movements build mountains, open oceans, and generate the world's most destructive natural events.
Almost all earthquakes and volcanoes occur at or near plate margins — the boundaries where two plates meet. There are three types, each producing different hazards:
When an oceanic plate meets a continental plate, the denser oceanic plate is forced downward into the mantle in a process called subduction. As it descends, friction between the plates generates enormous pressure. When that pressure is released suddenly, it sends seismic waves through the crust — an earthquake. The subducting plate also melts as it descends into the hot mantle, producing magma that rises to form volcanoes above. Example: The Nazca Plate subducting beneath the South American Plate produces both the Andes mountain range and Chile's devastating earthquakes.
When two continental plates converge, neither can subduct (both are too light). Instead they crumple upward, forming mountain ranges. The immense pressure still produces powerful earthquakes, but without subduction there is no magma and therefore no volcanoes. Example: The Indian Plate crashing into the Eurasian Plate has pushed up the Himalayas over 50 million years — and still generates Nepal's earthquakes today.
Here, two plates grind sideways past each other. No crust is created or destroyed, so there are no volcanoes. But the friction as plates lock and then suddenly release generates powerful earthquakes. Example: The San Andreas Fault in California, where the Pacific Plate slides northward past the North American Plate.
As plates pull away from each other, magma rises to fill the gap, creating new oceanic crust and forming volcanoes. Earthquakes here tend to be shallower and less powerful than at destructive margins. Example: The Mid-Atlantic Ridge, where the Eurasian and North American plates separate — Iceland sits on this boundary and experiences both regular earthquakes and volcanic eruptions.
When an earthquake occurs, energy radiates outward from the focus — the underground point of origin — as seismic waves. The point on the surface directly above the focus is the epicentre, which usually experiences the most intense shaking. Shallow-focus earthquakes (less than 70 km deep) cause more surface damage than deep-focus ones because the energy has less distance to travel before reaching buildings and people.