Variations in Landforms III - TVC

Wednesday 26th March

DO NOW:• You have 10 mins to complete yesterday’s task.

Level 2 Geography

Craters and Craters Lakes Craters and crater lakes are found in the mountain peaks region of the TVC because craters are formed by volcanic explosions from fissures and vents of a volcano. The mountain peaks region is the main area of volcanic vents and fissures, therefore meaning that most of the regions craters and crater lakes are found here, as the diagram shows. Within the craters and crater lakes found in the TVC there are still variations. For example Tongariro is considered a complex volcanic system with the mountain being made up of several craters (see diagram) due to several eruptions blasting from different areas of Mt Tongariro. Tongariro’s summit has the “North Crater” which is flat; formed by when a lava lake solidified. A small crater has since blasted through this, as can be seen in the diagram. Mt Ngauruhoe has one central crater formed at the summit of a virtually perfect cone. Mt Ruapehu’s summit has many vents as different eruptions have blasted through the mountain and created craters. There is one main Crater Lake that is currently the most active. Craters and crater lakes are generally not found in other parts of the TVC as there are no volcanic activity around the eastern and western slopes and western foothills.

Lava Flows Lava flows can be found on the mountain peaks and the western and eastern slopes of the TVC because these regions are closest to the volcanic vents. Lava flows are not found on the western foothills as there are no volcanic vents in that region of the TVC and they are too undulating for lava flows, off the three main mountains, to flow through. For instance, there are visible lava tongues flowing off Mt Ngauruhoe (as shown in the diagram) on the Eastern slopes from the Red Crater and on the Western slopes down the Mangatepopo valley. There are not as many lava flows on Tongariro and Ruapehu (and few even on Ngauruhoe) because ash eruptions are more frequent than lava eruptions. Eruptions trigger the lava flows and the viscosity of the lava often determines how far the lava will flow. Ngauruhoe is the youngest and most active of the three main volcanoes in the TVC, meaning that we see evidence of lava flows more on Ngauruhoe than Tongariro and Ruapehu. Ash, and vegetation are likely to have covered up ancient lava flows on these two respective volcanoes.

Notice the lava flows following the river pattern

Lahars Lahars are most common on Mt Ruapehu due to the active vents having large crater lakes over them and the snow and ice that surround the summit. Lahars are turbulent mixtures of water and volcanic debris which flow rapidly downslope. These can be triggered by eruptions and or by excessive rainwater and melting snow. The evidence of lahars is found mainly around streams and river channels as lahars tend to follow the same gradient as these. Due to the reduced viscosity, lahars tend to flow much further than lava flows, meaning that there are remnants of lahars on the western foothills for example at Tangiwai.

Lahars - this shows where the lahar was expected

to flow

V-shaped Valleys V-shaped valleys are found mainly around the western foothills because there is very little erosion by glaciers, lava and lahar flows due to the lower altitude. The V-shaped valleys occur because of rivers and streams cutting deeply into the land in areas with a steep gradient. The western foothills is an undulating area with many small hills and valleys. These small hills are the perfect environment for V-shaped valleys, as there are steep gradients for rivers to carve deeply into the land. These valleys will remain V-shaped valleys until an ice age means that glaciation will occur in these lower altitude areas or lahars flow into the rivers.

U-shaped ValleysU-shaped valleys are found on mainly on the Western slopes (although they have their origins in the mountain peaks area), with some occurring on the eastern slopes because they have been created by lava and lahar flows and ancient glaciers (during the ice age 100,000 years ago). For example, the most famous U-shaped valley in the TVC is the Mangatepopo Valley which has been created by both glaciation and lava flows. U-shaped valleys begin their life as a V-shaped valley, with streams and rivers cutting deeply into the soil (ash/tephra layers). If glaciation and lava and lahar flows occur, they do not simply cut deeply, but also widely which means that instead of a V shape being created, a U shape is created. This is shown in the diagram where after a period of glaciation the valley floor is much wider than the before. U-shaped valleys are not as common around the western foothills, as the lahars and lava flows and certainly the glaciers have not reached these areas to erode them in the same way.

Ring Plain The ring plain is found on the lower area of the eastern slopes and around the base of the western foothills because this there is a very visible plateau lying around the base of the mountains. This plateau is easily identified on the eastern slopes, particularly when standing on the Desert Road. The ring plain is an area of land that is generally flat, or has a very small gradient, as the Rangipo Desert does on the lower eastern slopes. Lahars are largely responsible for building ring plains around mountains because as the lahar meets the small gradient the mud and debris spreads across the land depositing its load, rather than eroding the mountain as it does on the mountain slopes.

Ring Plain

Glaciers Glaciers are found on the mountain peaks because of glaciers need extremely cold temperatures only found at high altitude. For example, Mt Ruapehu is the only mountain to have glaciers because it has a much higher elevation (2797m) than Mt Tongariro (1967m) and Mt Ngauruhoe (2287m) and therefore has the extreme coldness required for glaciation to occur. For instance the average temperature on Mt Ruapehu is 3-4°C (not including wind chill factor) whereas the average temperature on Ngauruhoe and Tongariro is 9°C and 11°C respectively. This means that glaciers are only found on Mt Ruapehu because of the climatic processes that occur at such extreme altitudes that can not be replicated in any other areas of the TVC unless another ice age was to occur. The diagram shows Mt Ruapehu’s five glaciers feeding of the summit of the mountain. These glaciers follow the gradient of the land and eventually turn into streams and then rivers.

Glaciers - notice the glaciers creeping off the summit. They are the blue areas around the crater lake on the map below.

Radial Drainage Patterns A radial drainage pattern can be seen around each of the three mountain peaks, the western and eastern slopes and the western foothills because the mountains generally cone-shaped. The radial drainage pattern that is seen in the diagram starts with the small streams at the peaks of the mountains. These streams eventually flow into rivers like the Tongariro or Whakapapa river. Due to the cone-shape of these mountains, the rivers all flow from a central point outwards.

Radial Drainage Pattern

Reflection…

What questions do we have?

In your essays/diagrams about spatial variation – you need to be able to explain WHERE and WHY there are these variations.This means that you need to be able to explain the processes that create these landforms.