So this is my first "official" graduate level paper (not counting the four that were rejected up to twice apiece that need to be re-written and resubmitted to various ecology & biology journals), I wrote it for "Environmental Geology" seminar. Hope you like it! Even if you don't like it, feel free to comment:
Volcanic Processes and Super-volcanoes: Facts and Prospects
Introduction: Volcano Basics
In this section, basics about volcanoes and predicting when they might be more apt to erupt are be covered. Marti & Ernst (2005) includes an excellent discussion of volcano basics, some of which will be covered here. Most of the volcanic activity on Earth is located on the boundaries, or near to them, of continental plates, and the type of plate often dictates what types of volcanism are most prevalent in the vicinity (Marti & Ernst 2005). There are three basic types of plate boundaries: divergent, convergent and transform. At divergent plate boundaries, there are mid-ocean ridges formed by volcanoes that extend some 70,000 kilometers (km) around the Earth and these are the most common of all volcanoes. These types of boundaries are essentially caused by friction and pull of two or more plates as they pull apart from each other. The mid-ocean ridges formed by divergent plate boundaries essentially form one large, uninterrupted chain of mountains. Due to their under ocean nature however, it is often hard for the common person to understand that virtually all the World's sea floors are thus composed of volcanic material. In Iceland and some parts of Africa (e.g., the Rift Valley), there are exposed divergent boundaries on land, but this is not very common (Marti & Ernst 2005). With convergent plate boundaries, the plates are actually moving toward each other and one of the plates is typically forced downward, forming a deep trench area (e.g., the Mariana Trench). There is some volcanic activity associated with these types of plates, as well as earthquakes that result from the forcing downward of one plate (called the descending plate). The last type of plate boundaries are transform plate boundaries, formed by plates moving past each other. In this situation, there tend to be some earthquakes but not as much volcanic activity as compare to the other two types (Marti & Ernst 2005).
Although most volcanism tends to occur under water (the mid-ocean ridge volcanism accounts for some 75% of all volcanic activity on Earth), the most interesting from our perspective are the volcanoes formed by convergent plate boundaries (Marti & Ernst 2005). These are the most well documented types of volcanic eruptions. The most active volcanic area is the so-called "Ring of Fire," an area composed largely of the edges of the rim of the Pacific Ocean. Although mid-ocean ridge formation is the most typical volcanic activity, we are often more aware of the subduction zone eruptions because they tend to be more explosive, and are located in areas habited, or close to habited areas, by humans (Marti & Ernst 2005). They virtually always form island arcs (e.g., the tops of under sea mountains that happen to protrude above sea level). Other important subduction zone volcanic activity is located: in the Atlantic Ocean (near the Lesser Antilles and Sandwich Island arcs) and in the Indian Ocean (the Indonesian island arc and the Aeolian and Hellenic island arcs) (Marti & Ernst 2005).
Another type of volcanism that occurs is called intraplate, in this type of volcanic activity, high rates of magma production due to unknown processes causes magma chamber formation. When the pressure is too great to be contained by its earthen top, the volcano erupts, emitting a magma plume (Mart & Ernst 2005). These volcanoes are often called "hotspots" and are believed to be formed over periods of millions of years by slow plate movement. They are thus often useful to geologists for inferring plate movements over geological time scales. Currently there are believed to be anywhere from 50 to 100 active hotspots around the world. Common classificatory features of hotspots are voluminous basaltic magma flows, abnormally high heat flow, thinning of overlying crust (e.g., crust above the magma chamber) and development over deep time of a topographic high. One example of a hotspot is in the middle of the Pacific plate, which is what the Hawaiian Islands were formed by, and there are similar sea mounts formed in this way in the South Pacific. Some hotspots due coincide with divergent plate boundaries, such as Iceland (Marti & Ernst 2005). The Yellowstone Caldera is an example of a very large hotspot, though as it is a supervolcano too we postpone discussion of its unique features till below.
The main feature of volcanoes is magma, and a large part of what determines their exclusivity, is their magma content (Marti & Ernst 2005). Magma is formed deep within the Earth and it involves the melting of solid material to produce a state of liquidity. One type of hypothetical magma generation is called "decompression" melting and refers to the theory that hot mantle from deeper in the Earth is bought into contact with lower pressure and temperature material during mid-ocean ridge formation and results in melting of portions of the lower temperature mantle (Marti & Ernst 2005). In the case of subduction volcanism, since cold rather than hot material (e.g., in the case of upwelling) is returning to the mantle there must be something at work to generate enough of a pressure and temperature difference to induce melting. Indeed, it turns out that subduction zone magma is probably caused by the hydration of oceanic crust at deep levels as parts of the newly generated sea floor cracks and fissures. These fissures allow exotic chemical reactions between sea water and basalt that lend themselves to the hydration of sea floor material (Marti & Ernst 2005). Over time, as other sea floor sinks and replaces other material, poorly understood reactions are believed to occur at high pressure and low temperature (due largely to temperature differences between source material and sea water) and magma is thus born. Though geologists are more agreeable on the mechanism of Mid-Ocean Ridge (MORB) magma formation, they are less agreeable on mechanisms of subduction zone magma formation (Marti & Ernst 2005).
Magma is generally a mixture of melt, suspended crystals and gaseous bubbles formed as the magma gets closer to the surface of the Earth (Marti & Ernst 2005). Most magmas have around 45 to 77% of their weight by volume in SiO2, however they also tend to contain small amounts of aluminum, calcium, iron, magnesium, potassium and titanium. Compositional differences in magma are simply a reflection of what types of source rock are being melted by the magma. Using SiO2, Na2O and K2O however allows us to construct a roughhewn scheme for classifying magmas. Silicic magma is usually less than 62% SiO2, intermediate magma is usually around 52-63% SiO2, basic magma is 45-52% SiO2 and ultra basic magma is <45% SiO2. Mid-ocean ridge volcanoes tend to emit intermediate magmas, as do hotspot volcanoes though they tend to have magma flows relatively different then mid-ocean ridges, suggesting a totally different mechanism of magmatic formation (Marti & Ernst 2005). Water, C2O, sulfurs and halogens (such as Cl and F) tend to be found in fair percentages in magma and it is often the water content that determines just how explosive eruptions tend to be. Essentially, water becomes dissolved at a certain pressure closer to the mantle and as it gets closer to crust material, the magma becomes more and more saturated. Finally, Marti & Ernst (2005) tell us, on eruption, there will be a violent degassing as the water is released as gas from the volcano and depending on how much H2O is dissolved in the magma, the explosion can be much more powerful. For example, along the mid-ocean ridges the weight of the water columns tends to prevent degassing, hence eruptions tend to be less violent and more slow and timely. However, in subduction zones, particularly those located on the surface of the Earth, there can be very, very high rates of saturation and thus relatively violent explosions. In reference to above, the magma released in the 1980 Mt. St. Helens eruption was determined to contain about 4.5% H2O content (Marti & Ernst 2005). Sulfur itself tends to be important as it the amount of sulfur aerosols can have important climatic consequences, as Case Study 2 will show. Hotspot magma production is also little understood, though it can be inferred from the chemical composition of new ridge material compared with other, lower elevation material, that mantle melting must be involved. In this case, it is believed that density differences deep in the mantle lead to spurts of eruptive material over time (Marti & Ernst 2005).
In the end though, the main thing that is important is for the magma to reach the surface and, hence, erupt (Marti & Ernst 2005). The main force concerned with magmatic ascent is buoyancy generated by the difference between melt and surrounding rock. Magma tends to crystallize en route to the surface as it loses heat to surrounding rock and seems to follow other thermodynamic conduits that are warmer than surrounding rock. Magma accumulation tends to take place in reservoirs up to tens of kilometers below the surface of the Earth. However, most eruptions that have been documented are from far closer than 10 kilometers (Marti & Ernst 2005). When the density of magma and surrounding rock is the same, shallow reservoirs form which slowly fill with more and more magma over time. Eventually, this "neutral" buoyancy (as it's called), cannot hold and the magma bursts forth in a violent rain of lava, rocks and other debris (often classified based on the size of the particles raining down). Unsurprisingly, the size of a given eruption is closely connected with how much magma is in the magma reservoir beneath the eruption opening, and its chemical composition (Marti & Ernst 2005).
Case Study 1: the Toba Super-Eruption
This event was perhaps THE catastrophe of human history: the whole human population may have been reduced to as little as 1,500 breeding pairs (or up to 5,000) following the Toba Supereruption in Indonesia (Rampino and Ambrose 2000; also see Ambrose 1998; Rampino & Self 1993). Proposed by Ambrose (Rampino & Ambrose 2000) as a possible explanation for the previously puzzling human genetic bottleneck, geologists now realize it very well may have been the single greatest catastrophe to affect humankind yet. The Toba Supereruption (also just referred to as the Toba Event) has been dated to have occurred approximately 73,500 years before the present (B.P). in Indonesia (Rampino & Ambrose 2000). It was the largest explosive eruption in the last several hundred thousand years: 2500 to 3000 cubic kilometers of magma were released, and Toba tephra layers have been identified as far away as India (some 3,000 kilometers away) (Gathorne-Hardy & Harcourt-Smith 2003). The initial rate of discharge of magma was recently estimated by Oppenheimer (2002) to be some ~7,000,000,000 kilograms per second. Oppenheimer placed this estimate at 1-3 orders of magnitude greater than the older estimates (Oppenheimer 2002). 1% of the Earth's entire surface was covered with fine-grained ash (see Mason et al 2004; Oppenheimer 2002), and it produced an astounding ~1,000,000,000,000,000 grams of fine dust that shot into the stratosphere, as well as H2SO4 aerosols that persisted for approx. 6 years (Gathorne-Hardy & Harcourt-Smith 2003). The aerosol loading is believed to have produced a so-called "volcanic winter" (similar to the "nuclear winter" scenarios of game theorists) with possible regional cooling of around 15 degrees Celsius and global cooling of around 3-5 degrees Celsius (Gathorne-Hardy & Harcourt-Smith 2003). According to Vazquez & Reid (2004), isotopic analysis of the Toba magma reveals that magma was building inside the volcano for about 150,000 years and around 35,000 years before the eruption the level and diversity of the magma began increasing rapidly.
Gathorne-Hardy & Harcourt-Smith (2003) state that the explosion probably eliminated all life within the immediate vicinity of the volcano. Heavy tephra falls would later also have knocked down trees and exterminated all mammals and birds (Gathorne-Hardy & Harcourt-Smith 2003). The modern distribution of animals, in their view, lends support to the notion that larger animals probably were only killed within a 350 kilometer radius of the explosion (Gathorne-Hardy & Harcourt-Smith 2003). The Toba eruption deposited glass shards around 63 microns in size (large for volcanic eruptions) to as far as 14 degrees South latitude (Oppenheimer 2002). The Toba eruption has been linked in some studies to a sharp SO4 ^2- peak in various ice cores and there may have been limited Global climate effects. For example, the Earth's weather was cooler for several centuries after the event, and worldwide temperatures are believed to have been 3-5 degrees Celsius lower as a result of the ash cloud (Gathorne-Hardy & Harcourt-Smith 2003) They state however, that they do not believe that the so-called "volcanic winter" hypothesis of Ambrose (Rampino & Ambrose 2000) is correct.
Ambrose, a biological anthropologist behind the Rampino & Ambrose (2000) paper, replied to the criticism of Gathorne-Hardy & Harcourt-Smith (2003) in Ambrose (2003). Based on the newest research, Ambrose says that the Toba eruption, at its minimum produced up to 800 cubic kilometers of dense rock equivalent (DRE) (a measure used to determine solid rock equivalence for eruptive ash volumes) of ash in the atmosphere, making it the number two sized eruption of the last 450 million years. The newest models show that its ash fall encompassed: the northeastern Arabian Sea (64 degrees east), the Indian Ocean (14 degrees south of the equator), northern India and Bangladesh (25 degrees north of the equator) and the South China Sea (about 113 degrees east). Thus, the area blanketed by the blast is much larger than previous estimates placed it (Ambrose 2003). Acharyya & Basu (1993) showed that 10 centimeter thick deposits in the Bay of Bengal, the Indian Ocean and all over India are in fact Toba material from its most recent eruption. They also showed that some 6 meter thick deposits of ash in central India are also Toba material (Acharyya & Basu 1993). The largest sulfur aerosol loads ever recorded are linked to the Toba eruption, and an immediate 1 degree Celsius temperature drop in the South China Sea alone has been linked to the Toba eruption ash fall (e.g., the ash suspended above the South China Sea blocked the direct sunlight by a massive degree) (Ambrose 2003). This sulfur peak, found in the Greenland GISP2 ice core, spans 6 to 7 years (the "volcanic winter") and is then followed by the largest atmospheric calcium dust levels ever recorded, most likely representing ash coated debris and the bodies of dead organisms, this peak lasts for some 200 years (Ambrose 2003). It is believed that the temperature around Greenland dropped more than 6 degrees Celsius quite rapidly. In fact, climatology experts believe that the cold period that started around the time of the Toba eruption lasted for 1000 to 2000 years (the "instant" Ice Age), and this is found in all the major cores dated to the Pleistocene (Ambrose 2003).
As to the human genetic bottleneck (essentially, all humans are genetically descended from some ancestor, ancestors, from ~74,000, implying some severe reduction in the human population at that time), which Gathorne-Hardy & Harcourt-Smith (2003) assert does not exist, or isn't as dramatic as many human evolutionary genetics specialists believe, Ambrose (2003) points out that virtually all specialists in this area believe that the human species suffered a severe setback of some sort approximately 75,000 thousand years ago (kya). This means that the human population dropped to a low of around 1,000 to 3,000 breeding pairs, and then later rose dramatically, some 10,000 to 20,000 years later, making all modern humans direct ancestors of a small, closely related set of humans (Ambrose 2003). More precisely, it seems that if we consider the 1,000 year instant ice age that the Toba Supereruption seems to have caused, and the longer, slow warm up later on, then 9% of the time of Homo sapiens on Earth have been lived under the shadow of some severe climate change that occurred about 74,000 years ago (Ambrose 2003). We do not here describe in great detail Ambrose's theory of the evolutionary implications for human and primate evolution in the aftermath of the Toba event in any great detail as these are well known (e.g., Rampino & Ambrose 2000, Ambrose 2003, Ambrose 1998 etc). Suffice it to say, Ambrose (Rampino and Ambrose 2000; Ambrose 1998) does claim that the so-called Upper-Paleolithic Explosion (~ 70,000kya) was directly precipitated by the Toba super-eruption in that there would have been severe natural selection for greater brain size, higher measures of g, general intelligence, and greater social cooperation to survive in the new, unpredictable and ultra-cool world that humans found themselves living in.
Case Study 2: The Yellowstone Super-Volcano
Perhaps the single biggest question that American and Canadian volcanologists ask is, when will the Yellowstone Super-volcano erupt again? What was the last Yellowstone eruption like? It is now well-established that approximately 80% of Yellowstone is actually on top of a massive caldera that has erupted several times in the Earth's geological past, it is also established that there is an eruption cycle which is now overdue. What geologists want desperately to know is: when Yellowstone erupts, what will it be like? How many people will die as an immediate result of the eruption and how many due to residual effects? What will the park look like? How will it affect the economy of the most powerful nation on Earth? This section will discuss such questions and more.
At this point, not much is known for sure about Yellowstone so we will here focus on modeling of its magma chamber, monitoring of its geothermal and hydrologic activities, as well as what some recent modeling of a possible explosion could do to the Earth's atmosphere. According to Lowenstern et al (2006) much of Yellowstone's activity has been traced to a hotspot that remains fixed relative to the North American plate (which is moving southwest). It was only discovered in the 1970s that Yellowstone had experienced large scale, violent, high VEI explosions in the past. In fact, the Yellowstone caldera is now thought to have risen over 80 centimeters since the 1920s. This information, combined with active geothermal activity and seismic activity, including thermal boiling features that are found on around 70 square kilometers of Yellowstone National Park, led scientists to realize that Yellowstone is actually an active volcano. Yellowstone also releases over 45,000 tons of CO2 per day and is thus one of the Earth's greatest sources of the substance (aside from human activities of course). Geoscientists do not know whether the continual activity is caused by cooling of the magma chamber or whether it is continually receiving fresh melt (Lowenstern et al 2006).
Seismic tomography studies indicate that there is possibly a large, banana type shaped area of semi-melt, and a smaller blob-type are of semi-melt, both near the great magma chamber (Lowenstern et al 2006). The studies also reveal the existence of gravitational anomalies (in particular, one generated by an ultra-low density mass) located just under the Yellowstone caldera. It is estimated that around 15,000 cubic kilometers of crystal-melt is lying in the magma chamber, at depths of between 8 and 18 kilometers (Lowenstern et al 2006). Though the authors do not believe that there is currently enough melt located under Yellowstone to trigger a massive eruption, it must be kept in mind that current resolutions for geophysical images are limited to 10 kilometers, so they're really not too sure just how much crystal-melt magma is underneath Yellowstone (Lowenstern et al 2006). Fortunately for us, the very recent imaging work of Vasco et al (2007) showed that there appears to be no "hidden" fault activity, i.e., the faults that are responsible for Yellowstone's behavior are indeed the ones we are already aware of. In the last 50 years there have been: up to 3,000 earthquakes per year, large scale mass uplift and subsidence of ground materials in any given year, release of up to 5 to 6 Giga Watts of water energy (as steam condensation and hot water discharge) and, as mentioned above, there are up to 45,000 tons of CO2 released per day (Lowenstern et al 2006). Uplift of 1 meter was documented, this occurred in the period 1923-1985, followed by 25 centimeter subsidence from 1985-1995, followed by more uplift (according to Husen et al 2003). All of this means that Yellowstone is a very active area that must be monitored closely, particularly given that no super-eruptions have occurred during recorded human history (Lowenstern et al 2006).
Geoscientists do not know precisely what to look for, but at least we're recording data now, before another super-volcano erupts. Although volcanic scientists are now monitoring sites such as Yellowstone, Lowenstern et al (2006) reminds us that there is the dual disadvantage of not knowing the precursor events and not having enough data on high-threat volcanoes in general. What does seem to be true is that, depending on the season of the eruption, the sulfate aerosol dispersal would be bad (read: possibly worse than the Toba Event's probable climatic impacts) (Timmreck & Graf 2006). Using certain GCM computer simulation protocols, Timmreck and Graf (2006) found that there could be, for example, up 6 times the observed levels of sunlight reflecting aerosols in the atmosphere as were estimated to have been released by the Pinatubo eruption of 1991. Previous models of this type addressed tropical volcanoes and Timmreck and colleagues had wondered, well, what would Yellowstone do if Pinatubo was a "bad" eruption? The Timmreck & Graf (2006) model assumed a 1,700 megaton volume of initial ash dispersal, though it is now suspected that the ash fall could blanket up to 10,000,000 square kilometers (Jones et al 2006). Keep in mind that this area happens to be roughly the area of the continental USA if you're wondering why it seems like an absurdly large area of ash deposit. Jones et al (2006) also found, in their model, using a similar approach as Timmreck & Graf (2006) with modified GCMs (Global Climate Models), that an ash blanket from Yellowstone could cause serious disruptions to global climate systems such as the El Nino Southern Oscillation. They caution, however, that ocean temperatures themselves would not be largely affected, though there would be a huge impact on terrestrial temperatures (Jones et al 2006). To summarize, geoscientists don't really know much about the climatic effects of eruptions of the magnitude such as Yellowstone's 640kya eruption event, and the last Toba eruption event, but all simulations show that the effects are probably beyond anything geoscience can currently comprehend.
Volcano Hazard "Management" Strategies
There are many dangerous phenomena associated with volcanic eruptions in general, such as lahar flows (Keys 2007), lava dome collapses that can trigger seismic events (aka earthquakes) and tsunamis (due to land and water displacement) (see Tapuani et al 2005; Taron et al 2007) and as such, it is imperative that governmental responses to volcanic hazards be swift when danger appears immanent. In Perry & Godchaux (2005), the authors discuss volcano hazard management strategies. Two factors make volcanoes particularly problematic from a policy perspective. One is that during seemingly non-active phases, people tend to encroach on volcanic areas and even build habitations right close to, or on, volcanoes (Perry & Godchaux 2005). Another major feature of volcanic hazards is that an active volcano may erupt several times during an eruption event (Perry & Godchaux 2005). Other unique hazards associated with volcano activity are: seismicity, lightning, lahars, pyrochlastic flows and eject such as ballistics and very large bombs (Perry & Godchaux 2005).
The easiest way to ensure that casualties and injuries are minimized when a future eruption event is forecast is to control access to tectonically active areas, including around the volcano's vicinity, and to ensure complete evacuation when necessary (Perry & Godchaux 2005). They mention that a major problem however for disaster planning in this regard is that people often initially disregard potential disaster warnings, unless they're seen as coming from a credible source (Perry & Godchaux 2005). Protective actions, such as warning people to stay inside and wear breathing protective gear (etc) are also to be utilized (Perry & Godchaux 2005). Communication between local emergency management specialists and geoscience specialists is key here, for local emergency management experts must be made aware as early as an eruptive event is predicted, just how severe the impact will be and how much must be done to protect residents from ash fall, pyrochlastic flow and ballistic projectiles (Perry & Godchaux 2005). The authors recommend having a very-interconnected hazards warning system, integrated at all levels of government (Perry & Godchaux 2005). Another measure that has been used, unsuccessfully, is the use of zoning to keep people away from volcanoes, the measures often are locally controlled though and so exceptions to the zoning restrictions tend to pop-up pretty fast (Perry & Godchaux 2005). In line with this finding, businesses near volcanoes- such as in Hokkaido, Japan- often depend more on tourists than on local patrons and hence are more resistant to visitor exclusion (Perry & Godchaux 2005). Regardless of whether visitors want to interact with a soon to be erupting volcano, the most effective way to make people aware of the danger seems to be repeated warnings at many different levels of communication (e.g., Federal, state and local levels) (Perry & Godchaux 2005). A final, important principle that Perry & Godchaux (2005) mention is that local inhabitants often base their assessment of hazards prediction reliability on the perceived connection of local hazards specialists with Federal level volcano experts. Thus, if the experts appear to have given accurate warnings in the past, and to have access to specialized volcanic and seismic instrumentation, locals will be more likely to perceive them to be "accurate" in their public warnings and admonitions (Perry & Godchaux 2005). We should also keep in mind, as the authors point out in the conclusion of their paper, that human means of limiting volcanic threats are essentially non-existent (Perry & Godchaux 2005).
One of the most interesting studies done relating to volcanoes outside the geological realm is that of Goto et al (2006). In this study, a group of clinical psychologists examined the mental status of a group of Japanese people who were evacuated from Miyake Island, Japan in 2000 prior to a massive eruption that destroyed most human habitation on the island (Goto et al 2006). Miyake Island is a small (~13, 720 acres) volcanic island south of Tokyo that undergoes serious eruptions 2 to 3 times per century (Goto et al 2006). An eruption commenced on July 8, 2000 at approximately 6:48pm which duration was about 7 minutes (Goto et al 2006). Later, the volcano continued to emit poisonous gases and by August 26, the Japanese government ordered a complete evacuation of the island to the Japanese mainland, which involved moving some 1326 residents and procuring disaster food and housing relief for them (Goto et al 2006). The evacuation lasted partially for more than 1 year and actually extended to February 1, 2005, at which point all island residents were allowed to return after being administered routine medical check-ups (Goto et al 2006).
Goto et al (2006) noted that a major impediment in disaster preparedness in general is that people often don't grasp the severity of their situation from its onset, existing in a state of disbelief (Goto et al 2006). One acute problem with understanding disaster effects on local residents is that traditional Japanese values make it taboo to discuss emotions in public (Goto et al 2006). The authors pointed out that the psychological effects of large disasters such as volcanic eruptions are similar to those of people in the United States: tendency toward neuroticism and tendencies toward physical afflictions such as difficulty sleeping (Goto et al 2006). Destroyed and badly damaged habitation areas were strongly associated with more severe symptoms, such as Post-Traumatic Stress Disorder (PTSD) (Goto et al 2006). There is some age stratification observed in previous studies of severe disasters, namely that older people (over 60) tended to show psychological disordering for a longer period after disaster mitigation, while younger people's psychological disordering tended to drop off after a period of about 8 weeks of disaster mitigation (Goto et al 2006). Though Goto et al (2006) were mainly interested in whether the severity of the volcanic event and the length of the Miyake Island residents' evacuation would be a good indicator of duration onset prediction and duration of symptoms of PTSD (which turned out to be true), it is relevant to our study because severe volcanic eruptions would undoubtedly influence human physical and mental health, as well as climatic conditions.
Conclusion
Volcanoes are amongst the most fascinating and feared of all natural phenomena found here on Earth, and they have probably influenced human history in ways we have yet to understand, with the Toba eruption being a prime example. As we have seen, the rare but humungous Super volcanoes are in a class by themselves in terms of the threat to human life, life in general and the Earth's climate they represent. Thus, we geoscientists must be ever vigilant to the threat that Yellowstone and other caldera systems pose, and keep the constant monitoring up.
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Volcanic Processes and Super-volcanoes: Facts and Prospects
Introduction: Volcano Basics
In this section, basics about volcanoes and predicting when they might be more apt to erupt are be covered. Marti & Ernst (2005) includes an excellent discussion of volcano basics, some of which will be covered here. Most of the volcanic activity on Earth is located on the boundaries, or near to them, of continental plates, and the type of plate often dictates what types of volcanism are most prevalent in the vicinity (Marti & Ernst 2005). There are three basic types of plate boundaries: divergent, convergent and transform. At divergent plate boundaries, there are mid-ocean ridges formed by volcanoes that extend some 70,000 kilometers (km) around the Earth and these are the most common of all volcanoes. These types of boundaries are essentially caused by friction and pull of two or more plates as they pull apart from each other. The mid-ocean ridges formed by divergent plate boundaries essentially form one large, uninterrupted chain of mountains. Due to their under ocean nature however, it is often hard for the common person to understand that virtually all the World's sea floors are thus composed of volcanic material. In Iceland and some parts of Africa (e.g., the Rift Valley), there are exposed divergent boundaries on land, but this is not very common (Marti & Ernst 2005). With convergent plate boundaries, the plates are actually moving toward each other and one of the plates is typically forced downward, forming a deep trench area (e.g., the Mariana Trench). There is some volcanic activity associated with these types of plates, as well as earthquakes that result from the forcing downward of one plate (called the descending plate). The last type of plate boundaries are transform plate boundaries, formed by plates moving past each other. In this situation, there tend to be some earthquakes but not as much volcanic activity as compare to the other two types (Marti & Ernst 2005).
Although most volcanism tends to occur under water (the mid-ocean ridge volcanism accounts for some 75% of all volcanic activity on Earth), the most interesting from our perspective are the volcanoes formed by convergent plate boundaries (Marti & Ernst 2005). These are the most well documented types of volcanic eruptions. The most active volcanic area is the so-called "Ring of Fire," an area composed largely of the edges of the rim of the Pacific Ocean. Although mid-ocean ridge formation is the most typical volcanic activity, we are often more aware of the subduction zone eruptions because they tend to be more explosive, and are located in areas habited, or close to habited areas, by humans (Marti & Ernst 2005). They virtually always form island arcs (e.g., the tops of under sea mountains that happen to protrude above sea level). Other important subduction zone volcanic activity is located: in the Atlantic Ocean (near the Lesser Antilles and Sandwich Island arcs) and in the Indian Ocean (the Indonesian island arc and the Aeolian and Hellenic island arcs) (Marti & Ernst 2005).
Another type of volcanism that occurs is called intraplate, in this type of volcanic activity, high rates of magma production due to unknown processes causes magma chamber formation. When the pressure is too great to be contained by its earthen top, the volcano erupts, emitting a magma plume (Mart & Ernst 2005). These volcanoes are often called "hotspots" and are believed to be formed over periods of millions of years by slow plate movement. They are thus often useful to geologists for inferring plate movements over geological time scales. Currently there are believed to be anywhere from 50 to 100 active hotspots around the world. Common classificatory features of hotspots are voluminous basaltic magma flows, abnormally high heat flow, thinning of overlying crust (e.g., crust above the magma chamber) and development over deep time of a topographic high. One example of a hotspot is in the middle of the Pacific plate, which is what the Hawaiian Islands were formed by, and there are similar sea mounts formed in this way in the South Pacific. Some hotspots due coincide with divergent plate boundaries, such as Iceland (Marti & Ernst 2005). The Yellowstone Caldera is an example of a very large hotspot, though as it is a supervolcano too we postpone discussion of its unique features till below.
The main feature of volcanoes is magma, and a large part of what determines their exclusivity, is their magma content (Marti & Ernst 2005). Magma is formed deep within the Earth and it involves the melting of solid material to produce a state of liquidity. One type of hypothetical magma generation is called "decompression" melting and refers to the theory that hot mantle from deeper in the Earth is bought into contact with lower pressure and temperature material during mid-ocean ridge formation and results in melting of portions of the lower temperature mantle (Marti & Ernst 2005). In the case of subduction volcanism, since cold rather than hot material (e.g., in the case of upwelling) is returning to the mantle there must be something at work to generate enough of a pressure and temperature difference to induce melting. Indeed, it turns out that subduction zone magma is probably caused by the hydration of oceanic crust at deep levels as parts of the newly generated sea floor cracks and fissures. These fissures allow exotic chemical reactions between sea water and basalt that lend themselves to the hydration of sea floor material (Marti & Ernst 2005). Over time, as other sea floor sinks and replaces other material, poorly understood reactions are believed to occur at high pressure and low temperature (due largely to temperature differences between source material and sea water) and magma is thus born. Though geologists are more agreeable on the mechanism of Mid-Ocean Ridge (MORB) magma formation, they are less agreeable on mechanisms of subduction zone magma formation (Marti & Ernst 2005).
Magma is generally a mixture of melt, suspended crystals and gaseous bubbles formed as the magma gets closer to the surface of the Earth (Marti & Ernst 2005). Most magmas have around 45 to 77% of their weight by volume in SiO2, however they also tend to contain small amounts of aluminum, calcium, iron, magnesium, potassium and titanium. Compositional differences in magma are simply a reflection of what types of source rock are being melted by the magma. Using SiO2, Na2O and K2O however allows us to construct a roughhewn scheme for classifying magmas. Silicic magma is usually less than 62% SiO2, intermediate magma is usually around 52-63% SiO2, basic magma is 45-52% SiO2 and ultra basic magma is <45% SiO2. Mid-ocean ridge volcanoes tend to emit intermediate magmas, as do hotspot volcanoes though they tend to have magma flows relatively different then mid-ocean ridges, suggesting a totally different mechanism of magmatic formation (Marti & Ernst 2005). Water, C2O, sulfurs and halogens (such as Cl and F) tend to be found in fair percentages in magma and it is often the water content that determines just how explosive eruptions tend to be. Essentially, water becomes dissolved at a certain pressure closer to the mantle and as it gets closer to crust material, the magma becomes more and more saturated. Finally, Marti & Ernst (2005) tell us, on eruption, there will be a violent degassing as the water is released as gas from the volcano and depending on how much H2O is dissolved in the magma, the explosion can be much more powerful. For example, along the mid-ocean ridges the weight of the water columns tends to prevent degassing, hence eruptions tend to be less violent and more slow and timely. However, in subduction zones, particularly those located on the surface of the Earth, there can be very, very high rates of saturation and thus relatively violent explosions. In reference to above, the magma released in the 1980 Mt. St. Helens eruption was determined to contain about 4.5% H2O content (Marti & Ernst 2005). Sulfur itself tends to be important as it the amount of sulfur aerosols can have important climatic consequences, as Case Study 2 will show. Hotspot magma production is also little understood, though it can be inferred from the chemical composition of new ridge material compared with other, lower elevation material, that mantle melting must be involved. In this case, it is believed that density differences deep in the mantle lead to spurts of eruptive material over time (Marti & Ernst 2005).
In the end though, the main thing that is important is for the magma to reach the surface and, hence, erupt (Marti & Ernst 2005). The main force concerned with magmatic ascent is buoyancy generated by the difference between melt and surrounding rock. Magma tends to crystallize en route to the surface as it loses heat to surrounding rock and seems to follow other thermodynamic conduits that are warmer than surrounding rock. Magma accumulation tends to take place in reservoirs up to tens of kilometers below the surface of the Earth. However, most eruptions that have been documented are from far closer than 10 kilometers (Marti & Ernst 2005). When the density of magma and surrounding rock is the same, shallow reservoirs form which slowly fill with more and more magma over time. Eventually, this "neutral" buoyancy (as it's called), cannot hold and the magma bursts forth in a violent rain of lava, rocks and other debris (often classified based on the size of the particles raining down). Unsurprisingly, the size of a given eruption is closely connected with how much magma is in the magma reservoir beneath the eruption opening, and its chemical composition (Marti & Ernst 2005).
Case Study 1: the Toba Super-Eruption
This event was perhaps THE catastrophe of human history: the whole human population may have been reduced to as little as 1,500 breeding pairs (or up to 5,000) following the Toba Supereruption in Indonesia (Rampino and Ambrose 2000; also see Ambrose 1998; Rampino & Self 1993). Proposed by Ambrose (Rampino & Ambrose 2000) as a possible explanation for the previously puzzling human genetic bottleneck, geologists now realize it very well may have been the single greatest catastrophe to affect humankind yet. The Toba Supereruption (also just referred to as the Toba Event) has been dated to have occurred approximately 73,500 years before the present (B.P). in Indonesia (Rampino & Ambrose 2000). It was the largest explosive eruption in the last several hundred thousand years: 2500 to 3000 cubic kilometers of magma were released, and Toba tephra layers have been identified as far away as India (some 3,000 kilometers away) (Gathorne-Hardy & Harcourt-Smith 2003). The initial rate of discharge of magma was recently estimated by Oppenheimer (2002) to be some ~7,000,000,000 kilograms per second. Oppenheimer placed this estimate at 1-3 orders of magnitude greater than the older estimates (Oppenheimer 2002). 1% of the Earth's entire surface was covered with fine-grained ash (see Mason et al 2004; Oppenheimer 2002), and it produced an astounding ~1,000,000,000,000,000 grams of fine dust that shot into the stratosphere, as well as H2SO4 aerosols that persisted for approx. 6 years (Gathorne-Hardy & Harcourt-Smith 2003). The aerosol loading is believed to have produced a so-called "volcanic winter" (similar to the "nuclear winter" scenarios of game theorists) with possible regional cooling of around 15 degrees Celsius and global cooling of around 3-5 degrees Celsius (Gathorne-Hardy & Harcourt-Smith 2003). According to Vazquez & Reid (2004), isotopic analysis of the Toba magma reveals that magma was building inside the volcano for about 150,000 years and around 35,000 years before the eruption the level and diversity of the magma began increasing rapidly.
Gathorne-Hardy & Harcourt-Smith (2003) state that the explosion probably eliminated all life within the immediate vicinity of the volcano. Heavy tephra falls would later also have knocked down trees and exterminated all mammals and birds (Gathorne-Hardy & Harcourt-Smith 2003). The modern distribution of animals, in their view, lends support to the notion that larger animals probably were only killed within a 350 kilometer radius of the explosion (Gathorne-Hardy & Harcourt-Smith 2003). The Toba eruption deposited glass shards around 63 microns in size (large for volcanic eruptions) to as far as 14 degrees South latitude (Oppenheimer 2002). The Toba eruption has been linked in some studies to a sharp SO4 ^2- peak in various ice cores and there may have been limited Global climate effects. For example, the Earth's weather was cooler for several centuries after the event, and worldwide temperatures are believed to have been 3-5 degrees Celsius lower as a result of the ash cloud (Gathorne-Hardy & Harcourt-Smith 2003) They state however, that they do not believe that the so-called "volcanic winter" hypothesis of Ambrose (Rampino & Ambrose 2000) is correct.
Ambrose, a biological anthropologist behind the Rampino & Ambrose (2000) paper, replied to the criticism of Gathorne-Hardy & Harcourt-Smith (2003) in Ambrose (2003). Based on the newest research, Ambrose says that the Toba eruption, at its minimum produced up to 800 cubic kilometers of dense rock equivalent (DRE) (a measure used to determine solid rock equivalence for eruptive ash volumes) of ash in the atmosphere, making it the number two sized eruption of the last 450 million years. The newest models show that its ash fall encompassed: the northeastern Arabian Sea (64 degrees east), the Indian Ocean (14 degrees south of the equator), northern India and Bangladesh (25 degrees north of the equator) and the South China Sea (about 113 degrees east). Thus, the area blanketed by the blast is much larger than previous estimates placed it (Ambrose 2003). Acharyya & Basu (1993) showed that 10 centimeter thick deposits in the Bay of Bengal, the Indian Ocean and all over India are in fact Toba material from its most recent eruption. They also showed that some 6 meter thick deposits of ash in central India are also Toba material (Acharyya & Basu 1993). The largest sulfur aerosol loads ever recorded are linked to the Toba eruption, and an immediate 1 degree Celsius temperature drop in the South China Sea alone has been linked to the Toba eruption ash fall (e.g., the ash suspended above the South China Sea blocked the direct sunlight by a massive degree) (Ambrose 2003). This sulfur peak, found in the Greenland GISP2 ice core, spans 6 to 7 years (the "volcanic winter") and is then followed by the largest atmospheric calcium dust levels ever recorded, most likely representing ash coated debris and the bodies of dead organisms, this peak lasts for some 200 years (Ambrose 2003). It is believed that the temperature around Greenland dropped more than 6 degrees Celsius quite rapidly. In fact, climatology experts believe that the cold period that started around the time of the Toba eruption lasted for 1000 to 2000 years (the "instant" Ice Age), and this is found in all the major cores dated to the Pleistocene (Ambrose 2003).
As to the human genetic bottleneck (essentially, all humans are genetically descended from some ancestor, ancestors, from ~74,000, implying some severe reduction in the human population at that time), which Gathorne-Hardy & Harcourt-Smith (2003) assert does not exist, or isn't as dramatic as many human evolutionary genetics specialists believe, Ambrose (2003) points out that virtually all specialists in this area believe that the human species suffered a severe setback of some sort approximately 75,000 thousand years ago (kya). This means that the human population dropped to a low of around 1,000 to 3,000 breeding pairs, and then later rose dramatically, some 10,000 to 20,000 years later, making all modern humans direct ancestors of a small, closely related set of humans (Ambrose 2003). More precisely, it seems that if we consider the 1,000 year instant ice age that the Toba Supereruption seems to have caused, and the longer, slow warm up later on, then 9% of the time of Homo sapiens on Earth have been lived under the shadow of some severe climate change that occurred about 74,000 years ago (Ambrose 2003). We do not here describe in great detail Ambrose's theory of the evolutionary implications for human and primate evolution in the aftermath of the Toba event in any great detail as these are well known (e.g., Rampino & Ambrose 2000, Ambrose 2003, Ambrose 1998 etc). Suffice it to say, Ambrose (Rampino and Ambrose 2000; Ambrose 1998) does claim that the so-called Upper-Paleolithic Explosion (~ 70,000kya) was directly precipitated by the Toba super-eruption in that there would have been severe natural selection for greater brain size, higher measures of g, general intelligence, and greater social cooperation to survive in the new, unpredictable and ultra-cool world that humans found themselves living in.
Case Study 2: The Yellowstone Super-Volcano
Perhaps the single biggest question that American and Canadian volcanologists ask is, when will the Yellowstone Super-volcano erupt again? What was the last Yellowstone eruption like? It is now well-established that approximately 80% of Yellowstone is actually on top of a massive caldera that has erupted several times in the Earth's geological past, it is also established that there is an eruption cycle which is now overdue. What geologists want desperately to know is: when Yellowstone erupts, what will it be like? How many people will die as an immediate result of the eruption and how many due to residual effects? What will the park look like? How will it affect the economy of the most powerful nation on Earth? This section will discuss such questions and more.
At this point, not much is known for sure about Yellowstone so we will here focus on modeling of its magma chamber, monitoring of its geothermal and hydrologic activities, as well as what some recent modeling of a possible explosion could do to the Earth's atmosphere. According to Lowenstern et al (2006) much of Yellowstone's activity has been traced to a hotspot that remains fixed relative to the North American plate (which is moving southwest). It was only discovered in the 1970s that Yellowstone had experienced large scale, violent, high VEI explosions in the past. In fact, the Yellowstone caldera is now thought to have risen over 80 centimeters since the 1920s. This information, combined with active geothermal activity and seismic activity, including thermal boiling features that are found on around 70 square kilometers of Yellowstone National Park, led scientists to realize that Yellowstone is actually an active volcano. Yellowstone also releases over 45,000 tons of CO2 per day and is thus one of the Earth's greatest sources of the substance (aside from human activities of course). Geoscientists do not know whether the continual activity is caused by cooling of the magma chamber or whether it is continually receiving fresh melt (Lowenstern et al 2006).
Seismic tomography studies indicate that there is possibly a large, banana type shaped area of semi-melt, and a smaller blob-type are of semi-melt, both near the great magma chamber (Lowenstern et al 2006). The studies also reveal the existence of gravitational anomalies (in particular, one generated by an ultra-low density mass) located just under the Yellowstone caldera. It is estimated that around 15,000 cubic kilometers of crystal-melt is lying in the magma chamber, at depths of between 8 and 18 kilometers (Lowenstern et al 2006). Though the authors do not believe that there is currently enough melt located under Yellowstone to trigger a massive eruption, it must be kept in mind that current resolutions for geophysical images are limited to 10 kilometers, so they're really not too sure just how much crystal-melt magma is underneath Yellowstone (Lowenstern et al 2006). Fortunately for us, the very recent imaging work of Vasco et al (2007) showed that there appears to be no "hidden" fault activity, i.e., the faults that are responsible for Yellowstone's behavior are indeed the ones we are already aware of. In the last 50 years there have been: up to 3,000 earthquakes per year, large scale mass uplift and subsidence of ground materials in any given year, release of up to 5 to 6 Giga Watts of water energy (as steam condensation and hot water discharge) and, as mentioned above, there are up to 45,000 tons of CO2 released per day (Lowenstern et al 2006). Uplift of 1 meter was documented, this occurred in the period 1923-1985, followed by 25 centimeter subsidence from 1985-1995, followed by more uplift (according to Husen et al 2003). All of this means that Yellowstone is a very active area that must be monitored closely, particularly given that no super-eruptions have occurred during recorded human history (Lowenstern et al 2006).
Geoscientists do not know precisely what to look for, but at least we're recording data now, before another super-volcano erupts. Although volcanic scientists are now monitoring sites such as Yellowstone, Lowenstern et al (2006) reminds us that there is the dual disadvantage of not knowing the precursor events and not having enough data on high-threat volcanoes in general. What does seem to be true is that, depending on the season of the eruption, the sulfate aerosol dispersal would be bad (read: possibly worse than the Toba Event's probable climatic impacts) (Timmreck & Graf 2006). Using certain GCM computer simulation protocols, Timmreck and Graf (2006) found that there could be, for example, up 6 times the observed levels of sunlight reflecting aerosols in the atmosphere as were estimated to have been released by the Pinatubo eruption of 1991. Previous models of this type addressed tropical volcanoes and Timmreck and colleagues had wondered, well, what would Yellowstone do if Pinatubo was a "bad" eruption? The Timmreck & Graf (2006) model assumed a 1,700 megaton volume of initial ash dispersal, though it is now suspected that the ash fall could blanket up to 10,000,000 square kilometers (Jones et al 2006). Keep in mind that this area happens to be roughly the area of the continental USA if you're wondering why it seems like an absurdly large area of ash deposit. Jones et al (2006) also found, in their model, using a similar approach as Timmreck & Graf (2006) with modified GCMs (Global Climate Models), that an ash blanket from Yellowstone could cause serious disruptions to global climate systems such as the El Nino Southern Oscillation. They caution, however, that ocean temperatures themselves would not be largely affected, though there would be a huge impact on terrestrial temperatures (Jones et al 2006). To summarize, geoscientists don't really know much about the climatic effects of eruptions of the magnitude such as Yellowstone's 640kya eruption event, and the last Toba eruption event, but all simulations show that the effects are probably beyond anything geoscience can currently comprehend.
Volcano Hazard "Management" Strategies
There are many dangerous phenomena associated with volcanic eruptions in general, such as lahar flows (Keys 2007), lava dome collapses that can trigger seismic events (aka earthquakes) and tsunamis (due to land and water displacement) (see Tapuani et al 2005; Taron et al 2007) and as such, it is imperative that governmental responses to volcanic hazards be swift when danger appears immanent. In Perry & Godchaux (2005), the authors discuss volcano hazard management strategies. Two factors make volcanoes particularly problematic from a policy perspective. One is that during seemingly non-active phases, people tend to encroach on volcanic areas and even build habitations right close to, or on, volcanoes (Perry & Godchaux 2005). Another major feature of volcanic hazards is that an active volcano may erupt several times during an eruption event (Perry & Godchaux 2005). Other unique hazards associated with volcano activity are: seismicity, lightning, lahars, pyrochlastic flows and eject such as ballistics and very large bombs (Perry & Godchaux 2005).
The easiest way to ensure that casualties and injuries are minimized when a future eruption event is forecast is to control access to tectonically active areas, including around the volcano's vicinity, and to ensure complete evacuation when necessary (Perry & Godchaux 2005). They mention that a major problem however for disaster planning in this regard is that people often initially disregard potential disaster warnings, unless they're seen as coming from a credible source (Perry & Godchaux 2005). Protective actions, such as warning people to stay inside and wear breathing protective gear (etc) are also to be utilized (Perry & Godchaux 2005). Communication between local emergency management specialists and geoscience specialists is key here, for local emergency management experts must be made aware as early as an eruptive event is predicted, just how severe the impact will be and how much must be done to protect residents from ash fall, pyrochlastic flow and ballistic projectiles (Perry & Godchaux 2005). The authors recommend having a very-interconnected hazards warning system, integrated at all levels of government (Perry & Godchaux 2005). Another measure that has been used, unsuccessfully, is the use of zoning to keep people away from volcanoes, the measures often are locally controlled though and so exceptions to the zoning restrictions tend to pop-up pretty fast (Perry & Godchaux 2005). In line with this finding, businesses near volcanoes- such as in Hokkaido, Japan- often depend more on tourists than on local patrons and hence are more resistant to visitor exclusion (Perry & Godchaux 2005). Regardless of whether visitors want to interact with a soon to be erupting volcano, the most effective way to make people aware of the danger seems to be repeated warnings at many different levels of communication (e.g., Federal, state and local levels) (Perry & Godchaux 2005). A final, important principle that Perry & Godchaux (2005) mention is that local inhabitants often base their assessment of hazards prediction reliability on the perceived connection of local hazards specialists with Federal level volcano experts. Thus, if the experts appear to have given accurate warnings in the past, and to have access to specialized volcanic and seismic instrumentation, locals will be more likely to perceive them to be "accurate" in their public warnings and admonitions (Perry & Godchaux 2005). We should also keep in mind, as the authors point out in the conclusion of their paper, that human means of limiting volcanic threats are essentially non-existent (Perry & Godchaux 2005).
One of the most interesting studies done relating to volcanoes outside the geological realm is that of Goto et al (2006). In this study, a group of clinical psychologists examined the mental status of a group of Japanese people who were evacuated from Miyake Island, Japan in 2000 prior to a massive eruption that destroyed most human habitation on the island (Goto et al 2006). Miyake Island is a small (~13, 720 acres) volcanic island south of Tokyo that undergoes serious eruptions 2 to 3 times per century (Goto et al 2006). An eruption commenced on July 8, 2000 at approximately 6:48pm which duration was about 7 minutes (Goto et al 2006). Later, the volcano continued to emit poisonous gases and by August 26, the Japanese government ordered a complete evacuation of the island to the Japanese mainland, which involved moving some 1326 residents and procuring disaster food and housing relief for them (Goto et al 2006). The evacuation lasted partially for more than 1 year and actually extended to February 1, 2005, at which point all island residents were allowed to return after being administered routine medical check-ups (Goto et al 2006).
Goto et al (2006) noted that a major impediment in disaster preparedness in general is that people often don't grasp the severity of their situation from its onset, existing in a state of disbelief (Goto et al 2006). One acute problem with understanding disaster effects on local residents is that traditional Japanese values make it taboo to discuss emotions in public (Goto et al 2006). The authors pointed out that the psychological effects of large disasters such as volcanic eruptions are similar to those of people in the United States: tendency toward neuroticism and tendencies toward physical afflictions such as difficulty sleeping (Goto et al 2006). Destroyed and badly damaged habitation areas were strongly associated with more severe symptoms, such as Post-Traumatic Stress Disorder (PTSD) (Goto et al 2006). There is some age stratification observed in previous studies of severe disasters, namely that older people (over 60) tended to show psychological disordering for a longer period after disaster mitigation, while younger people's psychological disordering tended to drop off after a period of about 8 weeks of disaster mitigation (Goto et al 2006). Though Goto et al (2006) were mainly interested in whether the severity of the volcanic event and the length of the Miyake Island residents' evacuation would be a good indicator of duration onset prediction and duration of symptoms of PTSD (which turned out to be true), it is relevant to our study because severe volcanic eruptions would undoubtedly influence human physical and mental health, as well as climatic conditions.
Conclusion
Volcanoes are amongst the most fascinating and feared of all natural phenomena found here on Earth, and they have probably influenced human history in ways we have yet to understand, with the Toba eruption being a prime example. As we have seen, the rare but humungous Super volcanoes are in a class by themselves in terms of the threat to human life, life in general and the Earth's climate they represent. Thus, we geoscientists must be ever vigilant to the threat that Yellowstone and other caldera systems pose, and keep the constant monitoring up.
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