Auckland is a volcanic hotspot which means that there is 52 volcanoes in the whole of Auckland.In Auckland the volcanic field is monogenetic. Monogenetic means that each volcano usually erupts once. Auckland’s volcanic field is still very much active and we have no way of telling when the magma will rise to create new volcanoes.
Basaltic lava also known as mafic lava is molten rock in which is embellished with magnesium and iron. If the mafic lava is mixed with either seawater or water from the ground and becomes heated steam It will blow it apart. If this happens it will become a pyroclastic eruption which Is when hot gas and volcanic matter moves down the volcano in a very fast manner reaching speeds of 700km/h and gases can reach to temperatures of 1000 degrees causing the eruption to be very explosive.
However when the magma doesn’t touch any water the lava can flow out less explosively and can build a tephra cone.The cause of Auckland’s volcanoes is the magma rising through the earth’s crust. When the tectonic plates move’s it releases the pressure causing the magma to rise to the surface, exploding causing an eruption. Over time the tectonic plates push land up, after multiple eruptions rocks build up causing a volcano to form.Auckland’s hot spot is an area of magma delivered from a plume of hot rocks rising out of the mantle (the hottest layer under the earth’s crust) .
In Auckland’s hot spot the temperature is so hot that the rocks are melting.A subduction zone is when one tectonic plate slides or bends under the other plate causing it to be bending into the mantle. The way Mangere Mountain was formed was because of the ‘bubble’ of magma rising through the earth’s crust. The magma had found contact with groundwater causing it to be a huge explosion which would of created a tuff ring. Fire fountaining then lava bursting up to the air creating steep mounds into the mountain. Vents threw out more scoria cones and they were so large it created another crater, making two craters in the mountain altogether.The lava dome on Mangere Mountain is a volcanic surface feature it was caused from the eruption 70,000 years ago from the magma flowing onto the surface of the volcano then filling up around the vent.
The magma doesn’t have enough pressure or gas to actually push it out causing the lava to sit pilling up on the vent. During the process the lava forms a plug which then gets pushed up by the magma underneath. It then creates a dome shape.The volcanic bombs were caused when the mountain was erupting and throwing out hot blocks of lava. Volcanoes can produce volcanic bombs which are thrown up and out a few kilometers but cools down in the air before it hits the ground. Which creates a rock and is still on Mangere Mountain today.lava tubes is a tunnel created by lava flow that is now solid.