1.0 Abstract:

This report investigates the largest active volcano in the world, the Yellowstone volcano. Volcanic landforms in general are initially described. Then it focuses on how this volcano has formed a caldera, and on the characteristic cauldron-like structure and its composition of basaltic and rhyolitic magma. Each individual landform, such as the Yellowstone Caldera volcano, is formed by specific processes and present distinct interactions with their surrounding environment. This as well as the rarity of it as a landform will be discussed in this report.

2.0 Table of contents:

Title page: ………………………………………………………………...p1
1.0 Abstract: ......................................................................................p2
2.0 Table of contents: ………………………………….……………..…p2
3.0 Introduction: …………………………………………….………..…..p3
4.0 Structure and composition of Yellowstone volcano: ………….…p3-p4
5.0 Yellowstone volcano processes: ……………………………….….p4-p5
6.0 Yellowstone volcano interactions: …………………………….…...p5-p6
7.0 Rate of recurrence of caldera volcanoes as a landform: ……….p6
8.0 Conclusion: …………………………………………………………..p6
9.0 References: …………………………………………………………..p7

3.0 Introduction:

The purpose of this report is to research and present reliable and detailed information on the Yellowstone caldera volcano. Through the examination of a range of published journal articles and internet sites on the topic of volcanic landforms, and more specifically on the Yellowstone caldera volcano, this report describes the Yellowstone caldera landform and goes into detail on four main topics of the volcano. These topics include the structure and composition of the selected volcano, its specific processes as a landform, how it interacts with other landforms or systems, and the rate of recurrence for similar landforms.

Landforms are features on the earth’s surface that are part of the terrain (Evans 2012, p. 95). Some of the main landforms include mountains, cliffs, valleys and craters (Evans 2012, p. 95). However, it is not limited to these a landform can also be defined by a vast range of other earth systems (Evans 2012, p. 95). Some of these features present more than one identity for example: large volcanoes are at the same time considered to be mountains, and other volcanoes can sometimes be islands, on the other hand many mountains and islands aren’t classified as volcanoes (Thouret & Nemeth 2011, p.1). Volcanic processes are quite complicated and diverse this is why they can create numerous landforms and have such a significant effect on the environment around them (Thouret & Nemeth 2011, p.1). Prolonged activity or even a singular volcanic eruption could result in the alteration of surrounding landscape at a local or regional scale (Oppenheimer, Martí & Ernst 2009, p.157). Volcanoes can be formed by interactions that occur between many different earth systems and processes, and changes that occur over time at particular rates (Oppenheimer, Martí & Ernst 2009, p.157). They can be described with reference to their existing features and how they originated, as well as by the way they develop and by the current changes that they may be experiencing (Evans 2012, p. 97). This report will focus on those specific to the Yellowstone caldera volcano.

4.0 Structure and composition of Yellowstone volcano:

Yellowstone volcano is the largest active volcano in the world, thus it has been named a supervolcano and it contains a huge amount of constantly moving molten rock comparable in size to Mount Everest (Lü et al. 2013, p 283). This supervolcano has had three eruptions that have formed calderas over the last 2 million years (Lü et al. 2013, p 283). Firstly, what is a caldera? A caldera is a depression, in an area of volcanic activity, which has a larger diameter than that of the potentially explosive volcanic craters or vents (Acocella 2007, p126). Calderas and volcanic craters can sometimes be confused with one another, the difference is the sizes that they present, a caldera is a depression with diameters that are over 1 kilometre whereas a volcanic crater is a circular depression with diameters that are usually less than 1 kilometre (Acocella 2007, p126). The Yellowstone caldera forms a piston-like structure and is over 60 kilometres in diameter (Lü et al. 2013, p 284).

The Yellowstone caldera is located in the Yellowstone national park in the USA and takes up most of the national park (Lü et al. 2013, p 287). This national park is considered a hot spot, located on top of a high plateau and having a hot mantle plume as support (Lü et al. 2013, p 287). The Yellowstone caldera is composed of both a large rhyolitic system and basaltic system (Lü et al. 2013, p 285). The basaltic magmas are formed at depth from the mantle and the rhyolitic magmas are generated by the melting of the continental crust (Lü et al. 2013, p 285). This creates ponds of gas rich felsic magmas ready to erupt (Lü et al. 2013, p 285).

5.0 Yellowstone volcano processes:

The processes involved in the formation of volcanoes can take millions of years. Many volcanoes form at the constructive or destructive plate boundaries, however some other volcanoes occur in the middle of plates, far from these boundaries (Thouret & Nemeth 2011, p.3). Yellowstone volcano is one of these that don’t occur at a plate boundary. To explain the formation of these types of volcanoes it is believed that inside the earth there are hot spots where hot rocks from near the core rise up through the mantle, melt near the surface and burn through the crust to form volcanoes (Thouret & Nemeth 2011, p.3). In the case of Yellowstone volcano the hot spot created a caldera.

The Yellowstone caldera was formed around 0.64 million years ago and is the youngest in a series of large calderas that were formed by massive eruptions that began around 16 million years ago (Wicks et al. 2006, p72). The processes involved in the formation of the caldera are quite simple. The magma that is located below the volcano provides a partial support for the volcano, particularly through the heat and buoyancy of magma (Wicks et al. 2006, p72). Thus when a large amount of magma is expelled due to an eruption, the support that it provided for the volcano is removed generating a collapse that in turn creates a caldera (Wicks et al. 2006, p72). This process explains how the Yellowstone caldera was formed. Once a caldera is formed by an eruption the volcanic system may have resurgent domes that appear in the caldera due to other smaller eruptions, this is called the caldera cycle (Wicks et al. 2006, p72). Furthermore, a ring fracture is produced by the collapse of the caldera, this area of fractures at the caldera edges then becomes weak zones (Wicks et al. 2006, p72). This means that the collapsed area of the Yellowstone caldera loses the support that was generated by the magma chamber and the crust.

The Yellowstone caldera is composed of a rhyolitic and basaltic system which further explains its formation (Wicks et al. 2006, p72). The mantle plume that is located under Yellowstone formed basaltic magma by partial melting which rose towards the surface melting the continental crust and producing the rhyolitic magma present in the Yellowstone caldera volcano (Wicks et al. 2006, p72). These felsic magmas are located in shallow chambers under Yellowstone and are ready to erupt up the ring fractures (Wicks et al. 2006, p72). The rhyolitic magma chambers are those that get depleted and cause the collapse and formation of calderas, such as the Yellowstone caldera, during caldera forming eruptions (Wicks et al. 2006, p72).

Currently the Yellowstone caldera is experiencing many processes due to the caldera cycle but this happens at a slow rate. The mallard lake dome and the sour creek dome are both resurgent domes that are located in the Yellowstone caldera, this is a clear sign of the caldera cycle being at work (Lü et al. 2013, p 286). An eruption that took place from around 150,000 to 70,000 years ago buried a large portion of Yellowstone caldera under flows of rhyolite lava (Wicks et al. 2006, p72). Since this eruption Yellowstone has been persistent, with high levels of seismic activity, continual occurrences of uplift and subsidence of the caldera, and hydrothermal activities of extreme force (Lü et al. 2013, p 283). In the past, periods of uplift and/or subsidence have been related to a number of different combinations of the following processes. The first process being pressurisation and de-pressurisation of hydrothermal chambers in the caldera, and the second being the way basaltic and rhyolitic magma moves, forms and crystallises (Wicks et al. 2006, p72). In the case of Yellowstone caldera it is more likely that magmatic processes are responsible for the uplift and subsidence experienced (Wicks et al. 2006, p74). The rupturing of a sealed hydrothermal chamber should form increases in the amount of chloride flux at the caldera surface (Wicks et al. 2006, p74). As there is no noticeable chloride flux related to periods of deformation in the caldera, it is most likely due to processes of magmatic source deformation rather than hydrothermal deformation (Wicks et al. 2006, p74). The magmatic source deformation involves the continual movement that occurs within the Yellowstone volcano structure of basalt molten (Wicks et al. 2006, p74). An increased amount of basalt molten into the caldera system from below will result in the inflation, uplift, of the caldera, whereas the decrease of basaltic magma will make for subsidence (Wicks et al. 2006, p74). One of the more important forces acting upon the movement of basaltic magma is its buoyancy and usually vertical gradient (Wicks et al. 2006, p74).

6.0 Yellowstone volcano interactions:

The Yellowstone volcano has the capability of creating new or destroying existing landforms, and to disrupt surrounding systems. During eruptions volcanoes can generate a range of variations in the climate (Cole‐Dai 2010, p824). Energy in the climate system determines what the earth’s climate is like (Cole‐Dai 2010, p824). To maintain a stable climate the earth must have an energy steady state in terms of incoming and outgoing radiation, and there must be a balanced circulation of energy between earth systems (Cole‐Dai 2010, p824). When an eruption occurs the volcano will expulse solid and gaseous volcanic emissions, ash clouds that form from the eruption can block sunlight and therefore reduce the amount of solar energy transferred to the earth’s surface (Cole‐Dai 2010, p825). Primarily, the eruption will cause the earth’s reception of solar energy to be reduced, as sulfate aerosols scatter incoming solar radiation (Cole‐Dai 2010, p824). Normally the effect of an eruption on the climate is relatively short lived with a duration limited to a few years following the eruption (Cole‐Dai 2010, p830). However, Yellowstone caldera is a supervolcano and is capable of super eruptions which could result in a long term climate impact, one possible outcome is the starting of glaciation and leading the way to an ice age (Cole‐Dai 2010, p831).

Furthermore, Volcanoes such as Yellowstone caldera can have very diverse interactions with other landforms and systems when active. A volcanic eruption can be very destructive to landforms and systems but it can also create new landforms (Oppenheimer, Martí & Ernst 2009, p157). When lava flows out of the volcanic system it will can accumulate in a particular place and make a landform such as a mountain, also as the lava flows in a particular direction in can destroy extensive flora and fauna (Oppenheimer, Martí & Ernst 2009, p157). Additionally, the seismic nature of the volcano can create valleys and the resulting earthquakes may also cause erosion to other surrounding mountains depending in its magnitude (Lü et al. 2013, p 289).

7.0 Rate of recurrence of caldera volcanoes as a landform:

The frequency of occurrence for caldera volcanoes is not as high as other volcanoes such as shield volcanoes and stratovolcanoes (Cole, Milner & Spinks 2005, p2). A caldera volcano may be fairly rare among the other types of volcanoes, because to form a caldera such as the Yellowstone volcano there needs to be an eruption powerful enough to create a collapse in the volcanic system, and there are not many volcanoes with this capability (Cole, Milner & Spinks 2005, p4). This is why caldera volcanoes tend to be the most powerful and catastrophic volcanoes in the world.

8.0 Conclusion:

This report clearly shows the attributes that make Yellowstone caldera volcano a landform. The Yellowstone volcano presents a cauldron-like structure moulded by specific processes. It can also be seen through this report that the composition of this volcano, basaltic and rhyolitic magma, acts upon the volcanic system in such a way as to eventually cause a collapse that results in the formation of a caldera like the Yellowstone caldera. Additionally, supervolcanoes such as the one selected can have interactions that may impact greatly landforms and systems within its eruptive reach, thus this interaction depends on the level of activity and power of the eruptions. Finally, caldera volcanoes can be seen to be rare due to the powerful processes needed to form one.

9.0 References:

Acocella, V. 2007, "Understanding caldera structure and development: An overview of analogue models compared to natural calderas", Earth Science Reviews, vol. 85, no. 3, pp. 125-160.
Cole, J.W., Milner, D.M. & Spinks, K.D. 2005, "Calderas and caldera structures: a review", Earth Science Reviews, vol. 69, no. 1, pp. 1-26.
Cole‐Dai, J. 2010, "Volcanoes and climate", Wiley Interdisciplinary Reviews: Climate Change, vol. 1, no. 6, pp. 824-839.
Evans, I.S. 2012, "Geomorphometry and landform mapping: What is a landform?", Geomorphology, vol. 137, no. 1, pp. 94-106.
Lü, Y., Ni, S., Xie, J., Xia, Y., Zeng, X. & Liu, B. 2013, "Crustal S-wave velocity structure of the Yellowstone region using a seismic ambient noise method", Earthquake Science, vol. 26, no. 5, pp. 283-291.
Oppenheimer, C., J, G G J Martí & Ernst 2009, "Volcanoes and the Environment", Geological Magazine, vol. 146, no. 1, pp. 157.
Thouret, J. & NÉmeth, K. 2011, "Special Issue on volcano Geomorphology ‘Landforms, processes and hazards’: Introduction", Geomorphology, vol136, no. 1, pp. 1-5.
Wicks, C.W., Thatcher, W., Dzurisin, D. & Svarc, J. 2006, "Uplift, thermal unrest and magma intrusion at Yellowstone caldera", Nature, vol. 440, no. 7080, pp. 72-75.