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Tectonic Hazards

Primary volcanic hazards

  • 3 things to know
  • Component 3 Section A

Overview

Primary volcanic hazard, pyroclastic flow and lava flows as a hazard.

What you need to know

Answer each one before you reveal it.

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Key term

Define a primary volcanic hazard.

Key term

What is a pyroclastic flow?

Key term

Why are pyroclastic flows the deadliest volcanic hazard?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define a primary volcanic hazard.

    Model answer

    A primary volcanic hazard is caused directly by the eruption itself. Lava flows, pyroclastic flows, ash falls, volcanic bombs and gas emissions are all primary hazards.

  2. 2

    What is a pyroclastic flow?

    Model answer

    A pyroclastic flow is a fast, ground-hugging current of hot gas, ash and rock fragments. Temperatures can exceed 500 °C and speeds commonly pass 100 km h⁻¹.

  3. 3

    Why are pyroclastic flows the deadliest volcanic hazard?

    Model answer

    A pyroclastic flow is too fast to outrun and kills by heat, asphyxiation and impact. Survival within the path of a flow is almost impossible.

  4. 4

    Give a named example of deaths caused by a pyroclastic flow.

    Model answer

    Pyroclastic flows from Soufrière Hills on Montserrat killed 19 people on 25 June 1997. The victims had returned to farm inside the exclusion zone.

  5. 5

    Describe lava flows as a hazard.

    Model answer

    Lava flows destroy everything in their path but usually move slowly enough for people to escape. Basaltic flows travel fastest because they are the least viscous.

  6. 6

    Give an example of an unusually fast lava flow.

    Model answer

    Nyiragongo in the Democratic Republic of the Congo produces exceptionally fluid, low-silica lava. Flows entering Goma in January 2002 destroyed much of the city centre and killed an estimated 150 people.

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