11SCI Volcano Internal

Describe the Auckland Volcanic Field. The Auckland Volcanic field was formed due to [blank_start]basalt magma[blank_end] coming from [blank_start]hot spot volcanism[blank_end] finding their way to the surface through [blank_start]fissures[blank_end] in the Earth’s [blank_start]crust[blank_end], causing violent [blank_start]phreatomagmatic explosions[blank_end] and eruptions. [blank_start]Basalt magma[blank_end] from [blank_start]hot spot volcanism[blank_end] has caused [blank_start]53[blank_end] volcanoes of different types in Auckland.

Name and describe specific features of the Onepoto volcano. Onepoto is a [blank_start]tuff ring[blank_end] volcano [blank_start]61[blank_end] meters deep and [blank_start]600[blank_end] meters wide. [blank_start]Basalt magma[blank_end] from a hot spot 100 km down formed Onepoto’s [blank_start]surface features[blank_end]. Onepoto used to be a crater that is now [blank_start]a flat bottom[blank_end] due to sediment buildup. The sides of the tuff ring is relatively steep, with a [blank_start]breach[blank_end] on the [blank_start]southwestern[blank_end] side due to [blank_start]human physical weathering[blank_end] and erosion to use for manmade purposes such as the construction of the harbor bridge and the roads leading up to the volcano. The tuff ring has plenty of [blank_start]trees[blank_end] on top of it.

Name and describe specific features of the North Head volcano. North head is a [blank_start]50m[blank_end] high, steep sided [blank_start]scoria cone[blank_end] on the [blank_start]North Shore of Auckland[blank_end]. It is the eroded remains of a scoria cone, [blank_start]scoria[blank_end] forming only on the top. [blank_start]Trees[blank_end] is apparent on the perimeter of the scoria cone. [blank_start]Exposed tuff ring[blank_end] beds are apparent on [blank_start]sea cliffs[blank_end]. The outwards sloping [blank_start]tuff beds[blank_end] form the shore platform around southern, eastern, and northern sides of the headland. A small stream of lava [blank_start]westwards[blank_end] the scoria cone is hidden beneath the houses in [blank_start]Takarunga road[blank_end]. [blank_start]Tunnels[blank_end] could be found in the firm, underlying [blank_start]tuff[blank_end] of the volcano for [blank_start]defense-related[blank_end] reasons, for purposes of making [blank_start]trenches[blank_end] to use as bunkers and tunnels lined with concrete and a concrete roof that was buried. The hill was weakly terraced by the pre-European Maori.

Discuss, in detail, how internal processes have contributed to the formation of the features you described in your chosen volcanoes. [blank_start]Basalt magma[blank_end] from a [blank_start]hotspot[blank_end] 100 kilometres down makes its way up, surfacing from a crack or a [blank_start]fissure[blank_end] in the Earth’s crust. As [blank_start]magma[blank_end] encounters [blank_start]cold groundwater[blank_end], steam is generated and pressure builds up, leading to a [blank_start]phreatomagmatic[blank_end] explosion. In a phreatomagmatic explosion, [blank_start]volcanic ash[blank_end] is thrown up into the air while heavier [blank_start]sediment[blank_end] is pushed [blank_start]horizontally[blank_end]. This creates a ring of [blank_start]wet ash[blank_end] and sediment that gradually hardens into a [blank_start]tuff ring[blank_end]. Time passes, and the volcano may stop erupting. Water would collect in the crater hole. At this point, tuff ring volcanoes like O[blank_start]nepoto[blank_end] and T[blank_start]ank Farm[blank_end] becomes extinct. However, some volcanoes like M[blank_start]ount Victoria[blank_end] and N[blank_start]orth Head[blank_end] continue to erupt. Additional lava rises in the vent and a [blank_start]lava lake[blank_end] is formed. If there is plenty of lava, fire / [blank_start]lava fountaining[blank_end] begins. [blank_start]Scoria cones[blank_end] start to build up around the vent. Lava / fire fountain continues, and scoria cones also continue to [blank_start]rise in height[blank_end]. Lava may burst out at a low level, like [blank_start]North Head[blank_end], flowing to fill the surrounding valleys and areas. The lava flow, like Mount Victoria, may have been so significant that it [blank_start]overcomes the stability[blank_end] of the scoria cone. The cone [blank_start]collapses[blank_end] into the lava flow and is carried away. This leaves a [blank_start]horseshoe-shaped breach[blank_end] in the crater.