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  • Stratovolcanoes are steep-sided, cone-shaped volcanoes. If the magma chamber within the volcano grows, the expansion can break the flanks of the volcano and cause it to collapse – creating a landslide. If the volcano is in the ocean – like Te Puia Whakaari/White Island or Indonesia’s Anak Krakatau – the debris can quickly displace/push a large volume of water and generate tsunami waves.

    Modelling a tsunami

    Landslides from stratocone volcanoes can generate tsunami waves. Use a balloon to model how a tsunami forms.

    Select here to view video transcript, questions for discussion and copyright information.

    In this activity, students use a balloon in a container of sand and water to model how volcanic eruptions can generate a tsunami.

    By the end of this activity, students should be able to:

    • demonstrate how magma chambers expand and the effects this expansion may cause
    • demonstrate how a horseshoe-shaped crater is formed by a lateral eruption
    • demonstrate how tsunami waves are generated by a landslide
    • identify Te Puia Whakaari/White Island and Anak Krakatoa volcanoes and tsunamis and discuss their formation.

    Download the Word file (see link below).

    Related content

    We have a wide range of related resources curated in these handy introductory articles below:

    Researchers discovered that the large underwater Hunga Tonga–Hunga Ha’apai volcano had a hidden caldera 150 m below the waves. Read about the devastating volcanic eruption in January 2022, the tsunami that followed and what we might expect next. Find out what scientists have discovered a year after this eruption in this article.

    Activity idea

    The Rotorua geothermal area was formed by a massive caldera. Watch the Rotorua caldera formation animation then go outside and conduct the student activity Calderas in the sandpit.

    Useful links

    The International Tsunami Information Center has information on the 2018 Anak Krakatau volcanic eruption. The before and after photos demonstrate the striking cone shape prior to the eruption and the horseshoe-shaped caldera after the eruption. This simulation shows the tsunami event that followed.


    This activity was developed by Kathleen Sibuea, a graduate student at the University of Canterbury. The activity uses a model developed by Dr Graham Leonard, a natural hazard scientist and geologist with GNS Science, and Professor Ben Kennedy at the University of Canterbury.

    The project received funding from GNS Science Beneath the waves.

      Published 28 February 2024 Referencing Hub articles
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