• Question: Why is the volcano wider at the bottom and smaller at the top?

    Asked by to Becky on 24 Jun 2014. This question was also asked by .
    • Photo: Rebecca Williams

      Rebecca Williams answered on 24 Jun 2014:

      Hi Claudia and denisa,
      This is such a great question!

      When a volcano erupts, it shoots ash, gas and rocks into the air. Think about when you throw a ball into the air – how often does it come straight back down to where it started from? Often, it lands a little way away from you. Now imagine throwing up 10 balls, or 100, or 10000. They would land all around you. If you kept doing this over and over again, eventually you’d build up a cone of balls with you in the middle. Some of the balls will roll away from you and others will land near you and stay there.

      Volcanoes are built up in the same way. When it erupts, some of the material settles close to the volcano and some of it falls further away. Because more volcanic rocks fall close to the middle, this bit gets taller and taller. Sometimes, lava will come out and flow from the middle, so it builds a layer of lava that is thick in the middle and thin at the edge. If you cut a volcano in half and looked inside, you’d see all these layers like this: http://whybecausescience.files.wordpress.com/2013/12/strato-volcano_composite-volcano.jpg?w=584

      Yesterday, I had some school children visit me and we made a volcano out of a bin! You can see how balls (imagine these are rocks) are spread around by an eruption in the video here https://www.youtube.com/watch?v=ZDLXo8HE45U&index=2&list=PLhJA5xYrlKbKY5B0TEbYWBZOYnd573Pip (this isn’t the video from yesterday, but its the same experiment).

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