Volcanic Landforms

Mt Ngauruhoe, a classic volcanic cone. Image: Julian Thomson.

Mt Ngauruhoe, a classic volcanic cone. Image: Julian Thomson.

New Zealand’s active volcanoes represent:

Volcanic Cones: The most well known volcanic landform features are the volcanic cones themselves. Mount Taranaki and Mount Ngauruhoe are classic symmetrical cones formed of alternating layers of lava and airborne debris (ash and scoria).

Crater Lakes: Eruption craters sometimes become filled with water to form lakes such as the Emerald Lakes of Tongariro and the crater lakes of Ruapehu and White Island. These crater lakes are quite rare globally, although we have some fine examples in New Zealand.

GNS Science staff monitoring the water of Mt Ruapehu's summit crater lake. Image: GNS Science, Agnes Mazot.

GNS Science staff monitoring the water of Mt Ruapehu's summit crater lake. Image: GNS Science, Agnes Mazot.

Lava flows: Lava flows solidify into lobe shaped features with very rough jagged surfaces and a layered cross section. Where they were flowing quite quickly, they may have developed side ridges or ‘levees’ that look similar to the artificial ‘stop banks’ made to prevent rivers from flooding. These superb examples of young lava flows can be seen in the Mangatepopo Valley at the start of the Tongariro Crossing. Different stages of revegetation on the different flows indicate their relative ages.

Red rocks are common around volcanoes and geothermal areas, and also found as layers within older greywacke sediments, such as at Red Rocks on the south coast of Wellington. They are evidence of the effect of hot geothermal fluids interacting with iron to create iron oxide (rust).

Lake Rotorua, a volcanic caldera. Image: GNS Science.

Lake Rotorua, a volcanic caldera. Image: GNS Science.

Calderas: Calderas are the devastated remains of the most violent of all volcano types. So much material was erupted from them that the emptied, cooled and contracted magma chamber below the volcano collapses in on itself to create an enormous ring shaped depression. Lake Taupo and Lake Rotorua are examples of calderas. Widespread pumice deposits from their past eruptions can be found in many parts of the North Island as well as in offshore drill cores.