From a Pile of Rice to an Avalanche: A Brief Introduction to Granular Materials

Catalyst Volume 9

Communities living at the foot of the Alps need a way to predict the occurrence of avalanches for timely evacuation, but monitoring the entire Alpine range is impossible. Fortunately for those near the Alps, the study of granular materials has allowed scientists to move mountains into labs and use small, contained systems (like piles of rice) to simulate real-world avalanche conditions. Granular materials, by definition, are conglomerates of discrete visible particles that lose kinetic energy during internal collisions; they are neither too small to be invisible to the naked eye, nor too big to be studied as distinct objects.¹ The size of granular material situates them between common objects and individual molecules.

While studying extremely small particles, scientists stumbled upon an unsettling contradiction: the classical laws governing the macroscopic universe do not always apply at microscopic scales. For example, Niels Bohr sought to apply classical mechanics to explain the orbits of electrons around nuclei by comparing them to the rotation of planets around stars. However, it was later discovered that an electron behaves in a much more complicated way than Bohr had anticipated. At its size, the electron gained properties that could only be described through an entirely new set of laws known as quantum mechanics.

Though granular materials do not exist at the quantum level, their distinct size necessitates an analogous departure from classical thought. A new category of physical laws must be created to describe the basic interactions among particles of this unique size. Intuitively, this makes sense; anyone who has cooked rice or played with sand knows that the individual grains behave more like water than solid objects. Scientists are intrigued by these materials because of the variation in their behaviors in different states of aggregation. More importantly, since our world consists of granular materials such as coffee, beans, dirt, snowflakes, and coal, their study sheds new light on the prediction of avalanches and earthquakes.

The physical properties of granular flow vary with the concentration of grains. At different concentrations, the grains experience different magnitudes of stress and dissipate energy in different ways. Since it is hard to derive a unifying formula to describe granular flows of varying concentrations, physicists use three sets of equations to fit their states of aggregation, resembling the gaseous, liquid, and solid phases. When the material is dilute enough for each grain to randomly fluctuate and translate, it acts like a gas. When the concentration increases, particles collide more frequently and the material functions as a liquid. Since these particles do not collide elastically, a fraction of their kinetic energy dissipates into heat during each collision. The increased frequency of inelastic collisions between grains in the analogous liquid phase results in increasing energy, dissipation, and greater stress. Finally, when the concentration increases to 50% or more, the material resembles a solid. The grains experience significant contact, resulting in predominantly frictional stress and energy dissipation.¹

Avalanches come in two types, flow and powder, each of which requires a specific combination of the gas, liquid, and solid granular models. In a flow avalanche, the descending layer consists of densely packed ice grains. The solid phase of granular materials best models this, meaning that friction becomes the chief analytical aspect. In a powder avalanche, particles of snow do not stick together and descend in a huge, white cloud.² The fluid and solid models of granular materials are equally appropriate here.

Physicists can use these avalanche models to investigate the phenomena leading up to a real-world avalanche. They can simulate the disturbance of a static pile of snow by constantly adding grains to a pile, or by perturbing a layer of grains on the pile’s surface. In an experiment conducted by statistical physicists Dr. Daerr and Dr. Douady, layers of glass beads of 1.8 to 3mm in diameter were poured onto a velvet surface, launching two distinct types of avalanches under different regimes decided by the tilt angle of the plane and the thickness of the layer of glass beads.³

For those of us who are not experts in avalanches, there are a few key points to take away from Daerr and Douady. They found that a critical tilt angle exists for spontaneous avalanches. When the angle of the slope remained under the critical angle, the size of the flow did not grow, even if a perturbation caused an additional downfall of grains. Interestingly, when the angle of the slope was altered significantly, the snow uphill from the perturbation point also contributed to the avalanche. That means that avalanches can affect higher elevations than their starting points. Moreover, the study found that the angle of the remaining slope after the avalanche was always less than the original angle of the slope, indicating that after a huge avalanche, mountains would remain stable until a change in external condition occured.³ A. Often, a snow mountain with slopes exceeding the critical angle can remain static and harmless for days, because of the cohesion between particles.

Situations become complicated if the grains are not completely dry, which is what happens in real snow avalanches. In these scenarios, physicists must modify existing formulas and conduct validating experiments to predict the behaviors of these systems. Granular materials are not limited to predicting avalanches. In geophysics, scientists have investigated the relation of granular materials to earthquakes. For instance, one study used sound waves and glass beads to study the effects of earthquake aftershocks.⁴ Apart from traditional modeling with piles of rice or sand, the understanding of granular materials under different phases paves the way for computational modeling of large-scale natural disasters like avalanches and earthquakes. These studies will not only help us understand granular materials themselves, but also help us predict certain types of natural disasters.

References

1. Jaeger, H. M., Nagel, S. R., and Behringer, R. P. Granular Solids, Liquids and Gases. Rev. Mod. Phys., 1996, 68, No.4, 1259-1273.
2. Frankenfield, J. Types of Spring and Summer Avalanches. http://www.mountain-guiding.com/avalanche/info/spring-types.html (accessed Oct. 29, 2015).
3. Daerr, A. and Douady, S. Two Types of Avalanche Behaviour in Granular Media. Nature, 1999, 399, 241-243.
4. Johnson P. A., et al. Effects of acoustic waves on stick–slip in granular media and implications for earthquakes. Nature, 2008, 451, 57-60.

Not Many Other Fish in the Sea: Our Current Overfishing Crises

Catalyst Volume 9

Prevailing notions of the ocean make it seem as if it is "too big to fail” since it takes up 70% of the surface of Earth and contains 321,003,271 cubic miles of water.¹ Additionally, most of the oceans’ immense biodiversity has yet to be documented. The Census of Marine Life estimates that there could be between 178,000 to 10,000,000 different species living in ocean shoreline habitats due to the vast abundance of photosynthesizing microbes.² However, like any ecosystem, the oceans are not immune to anthropogenic and environmental stressors such as overfishing, climate change, and pollution. There are many interconnected problems surrounding the way in which people currently treat the oceans. Extracting large amounts of fish for human consumption threatens the dynamic balance that currently exists and threatens scientists’ potential for making groundbreaking discoveries about what lies below.

In 2010, the United Nations predicted that over 80% of the world’s fish are reported as fully exploited or overexploited, and thus “require effective and precautionary management.”³ Overexploitation refers to the extraction of marine populations to unsustainable levels.4 Fishing techniques have become exponentially more efficient since the Industrial Revolution, focusing on getting the largest catches in the fewest trips. Today’s fishing fleets are so large that it would require two to three times Earth’s supply of fish to fill them.⁴ These harmful practices lead to three main types of overfishing:

1. Growth overfishing: The removal of larger fish leaves behind only individuals that are too small to maximize the yield, or full amount of fish that could theoretically be obtained.⁵
2. Recruitment overfishing: When adult fish are excessively taken out of the ecosystem, recruitment and stock productivity decreases.⁵
3. Ecosystem overfishing: The targeting of a particular species leads to serious trophic cascades and ecological consequences.⁵

Unfortunately, the most popularly consumed fish species are subject to all three practices. Bluefin tuna, sturgeon, sea bass, and Atlantic salmon are examples of large, long-lived predatory species that only provide a few offspring each breeding cycle.⁵ For example, Bluefin tuna release ten million eggs each year, but only a small number survive to adulthood. Even then, these tuna do not reach reproductive maturity until eight to twelve years of age.⁶ When the largest fish are specifically targeted, many ecological consequences arise. Removing the largest fish of the largest species in an ecosystem significantly decreases the mean size for that species. As a result, only smaller fish are left to reproduce.⁷ This shift causes trophic level decline: as species at higher trophic levels are overfished, fishermen decide to catch the comparatively larger fish at lower trophic levels.⁷ This vicious cycle continues so that the average size of fish consumed decreases significantly. This phenomenon, known as “eating down the food chain,” puts many fish at risk, including herbivorous fish in coral reef ecosystems.⁷ To maintain a coral-dominated state, herbivorous fish consume macro-algae that otherwise would overgrow and suffocate corals. When coral-dominated reefs become overtaken by macro-algae, habitats for many other fish and organisms are severely reduced. Over 25% of the world’s fish species live exclusively within these three-dimensional coral communities, which themselves only take up 0.1% of the ocean floor.⁵ Not only are species being depleted at the very top of the food chain, smaller species that are endemic to specific ocean environments are also indirectly experiencing survival pressure.

These problems are further magnified by the fact that current fishing practices produce a large amount of by-catch, or the incidental capture of non-target species.⁵ The rustic image of a humble fisherman using a single hook at the end of a line no longer reflects reality for most commercial fishermen. Now, longlines are weighted at the bottom and can have as many as 3,000 hooks attached, probing deeper into the water column.⁸ A similar weighted system exists for large fishing nets, known as trawl nets, so that shellfish and other small or bottom-dwelling organisms can be collected in larger quantities. Bottom trawling, the practice of dragging a trawl net across the ocean floor, has contributed to 95% of the damage inflicted on deep water systems by destroying and smothering benthic communities.⁹ These practices are non-specific in nature, and thus collect anything and everything that attaches or gets caught. Fishing gear alone has threatened around 20% of shark species with extinction and leads to over 200,000 loggerhead sea turtles deaths annually.¹⁰ Sylvia Earle, a renowned ocean-conservationist, describes these unsustainable fishing practices as “using bulldozers to kill songbirds.”¹¹

The United Nations now predicts that by 2050, the world will run out of commercially viable catches and oceans could turn fishless.³ Driving this problem is the fact that seafood consumption has increased over the past 30 years.¹² Many coastal communities and developing countries rely on fishing as their main source of income and protein, with approximately 2.9 million people relying on fish for over 20% of their animal protein intake. One of the largest importers, the United States, imports 91% (by value) from other countries with lower production costs.¹³ The cheap labor comes from subsistence fishermen, who meet this increased demand by opting for unsustainable practices. Consequently, a “poverty cycle” emerges, where short-term survival takes precedence over sustainability and conservation efforts, further exacerbating ecological and economic damages.¹⁴

Recognizing that environmental considerations alone could put many developing countries at risk, policymakers have adopted a community-based approach in the planning, construction, implementation, and management of preservation policies.¹⁵ This ecosystem approach to fisheries, strives to ensure that the capability of aquatic ecosystems to provide the necessary resources for human life is maintained for present and future generations.¹⁶

The establishment of Marine Protected Areas, or MPAs, is another effective technique similar to the National Park Service’s preservation programs. Although MPAs have a wide range of management plans and enforcement, all strive to limit or restrict human activity so that natural populations can be restored.⁵ Allowing an environment to restore its fish populations without any human mitigation can take a long time, and the most effective MPAs extend across large tracts of area that can more fully encompass fish populations and migratory species.⁵ Because these areas often overlap with highly profitable fishing zones, MPAs are regularly met with backlash from coastal communities and later can be hard to enforce.¹⁷

These international efforts to reduce the amount of seafood extracted from ocean environments are generally invisible in a grocery store, so it is easy for consumers to engage passively with the food they see. However, recognizing the production, labor, and ecosystem that goes into fish and fish products (and all foods) is critical for maintaining the livelihood of the world’s natural environments. The ocean may seem vast, but there is not an infinite supply of resources that can meet current demands.

References

1. National Oceanic and Atmospheric Administration. http://oceanservice.noaa.gov/facts/oceanwater.html (accessed Oct. 31, 2015).
2. Smithsonian Institute. http://ocean.si.edu/census-marine-life (accessed Nov. 1, 2015).
3. Resumed Review Conference on the Agreement Relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks; United Nations: New York, 2010.
4. Marine Biodiversity and Ecosystem Functioning. http://www.marbef.org/wiki/over_exploitation (accessed Oct. 31, 2015).
5. Sheppard, C.; David,S.; Pilling, G. The Biology of Coral Reefs,1; Oxford University Press: 2009.
6. World Wildlife Foundation http://wwf.panda.org/what_we_do/endangered_species/tuna/atlantic_bluefin_tuna/ (accessed Nov. 1, 2015).
7. Pauly, D., et al. Science. 1998, 279, 860-863.
8. Food and Agriculture Organization. http://www.fao.org/fishery/fishtech/1010/en (accessed Feb. 25, 2016).
9. The Impacts of Fishing on Vulnerable Marine Ecosystems; General Assembly of the United Nations: Oceans and the Law of the Sea Division, 2006.
10. Monterey Bay Aquarium. http://www.seafoodwatch.org/ocean-issues/wild-seafood/bycatch. (accessed Oct. 31, 2015).
11. Saeks, Diane Dorrans. US oceanographer Dr. Sylvia Earle. Financial Times, Aug. 9, 2013.
12. The State of World Fisheries and Aquaculture; Food and Agriculture Organization; United Nations: Rome 2014.
13. Gross, T. ‘The Great Fish Swap’: How America Is Downgrading Its Seafood Supply. National Public Radio, Jul. 1, 2014.
14. Cinner, J. et al. Current Biology. 2009. 19.3, 206-212.
15. Agardy, T. M. ; Information Needs for Marine Protected Areas: Scientific and Societal; 66.3; Bulletin of Marine Science, 2000; 875-878.
16. Food and Agriculture Organization. http://www.fao.org/fishery/topic/13261/en (accessed Nov. 1, 2015).
17. Agardy, T.M.; Advances in Marine Conservation: The Role of Marine Protected Areas; 9.7; Trends in Ecology and Evolution, 1994; 267-270.

Megafires

Catalyst Volume 9

In 2015, American forests were ravaged by larger and more destructive fires than ever before. One of the most devastating wildfires occurred in Washington State and burned over 250,000 acres of forest at a rate of 3.8 acres per second.¹ These unprecedented grand burns of over 100,000 acres have been justifiably coined by researchers as “Megafires.”² Unfortunately, megafires are becoming an increasingly common feature of the American West.

Although forest fires are a natural and essential part of a forest’s life cycle, scientific records show a worrisome trend. Data from the National Climate Center in Asheville, North Carolina indicate that recent fires burn twice the forest acreage as wildfires 40 years ago.³ In contrast to replenishing wildfires that promote forest growth, megafires scorch the landscape, disabling forest regeneration and leaving wastelands in their wake.² In other words, they burn forests so completely that trees are unable to regrow.⁴ The increased incidence of megafires accordingly threatens to cause environmental change, particularly in the Western United States.⁵ Once-rich forests are now in danger of depletion and extinction as they give way to grasslands and shrubs. Even the hardy Ponderosa Pine, previously thought to be completely flameproof, is succumbing to megafires.⁵

What is the future of our forests, and what can we, as custodians of our natural lands, do to shape this future? Can we prevent megafires? Understanding the contributing causes of megafires is essential in devising a solution to prevent them. Current thinking by various ecologists identifies three primary causative factors, both behavioral and environmental: new firefighting strategies, the rise of invasive species, and climate change.¹

Government policies that promote aggressive control of forest fires are deceptive in their benefits. Fire-fighters have become incredibly efficient at locating and extinguishing wildfires before they become too destructive. However, certain tree species that have flame- and temperature-resistant properties, such as the Pine Barrens, Lodgepole Pine, and Eucalyptus, require periodic fires in order to reproduce.⁶ When facing wildfires these types of trees survive, whereas other plant species perish. Since flame-resistant tree species are often native flora to forest ecosystems, the selective survival of these trees maintains the forest’s composition over time and prevents shrubs and grasslands from overrunning the ecosystem. Flame-resistant trees accomplish their phoenix-like regeneration and self-sustainability by releasing their seedlings during a wildfire. In addition, forest fires destroy flora that would impede the growth of new seedlings through competition for space and light. This regenerative effect of forest fires has even resulted in the return of certain endangered tree species.⁴ One example, the Jack Pine, maintains its seedlings in cones that melt in the presence of fire. A policy to extinguish fires prematurely can inhibit seed release, threatening Jack Pine forests and others like it.⁶ To date, aggressive government policies toward forest fire-fighting have led to significant changes in forest composition accompanied by buildup of tinder and debris on the forest floor. This accumulated undergrowth now fuels megafires that burn with unparalleled intensity and speed. In contrast, forest management policies that revert to the practice of allowing small, controlled fires to clear away debris would maintain the forest’s long-term survival.

Invasive, flame-susceptible species provide the perfect fuel for megafires. During their westward expansion in the 1880s, settlers were not the only ones to achieve Manifest Destiny. Several species of grass also made the journey. The most common of these species was the Cheatgrass, a grass native to Europe, southwestern Asia, and northern Africa.⁷ Cheatgrass was inadvertently brought to the Americas on cargo ships in the 1800s and has been a significant environmental problem ever since. The short life cycle and prolific seed production of Cheatgrass causes it to dry out by mid-June, meaning that it serves as kindling for fires during the summer. Cheatgrass increases the size and severity of fires since it burns twice as much as the endogenous vegetation.⁷ Since the native vegetation is slowly being choked out by Cheatgrass, the landscape of the American West is transitioning into a lawn of this invasive species, poised to erupt into an inferno.

Global warming, one of the environmental causes of megafires, is perhaps an even more critical and challenging threat than invasive species. In 2015, forest fires ravaged more than 9 million acres of the Western mainland United States and Alaska.³ Studies of global warming demonstrate that every degree Celsius of atmospheric warming is accompanied by a four-fold increase in the area of forest destruction. Thus, the increase in global temperature is directly associated with the prevalence of megafires.⁸ Since the 1900s, the average temperature of the planet has increased by 0.6 degrees Celsius, primarily in the twenty-first century.⁹ Typically, severe fires burn less often at higher altitudes, due to cooler temperature and greater moisture levels, but as global temperatures increase, these areas become drier and more prone to forest fires. This warming of the climate contributes to massive burns that are fueled by centuries of forest debris and undergrowth.⁹ Climate change also contributes to a lack of precipitation, which further contributes to the expansion and intensity of forest fires. Wildfires themselves also contribute to climate change; as they continue to burn they emit greenhouse gases, which can contribute to accelerating global warming.⁹

Ultimately, due to poor policy practice, a destructive cycle is forming that serves as a catalyst to megafires. Finding long-term solutions that will prevent the occurrence of megafires will require policy adjustments at the regional, national, and international levels.⁶ Currently policies are changing, endorsing smaller burns to limit build up for megafire fuel. As more data is being introduced about global warming, efforts are being made to find more renewable forms of energy such as solar and wind.⁹ Ideally, this shift in resources will limit the increase in global temperatures and reduce the risk of megafires. Lastly research is being done to develop grasses that can out compete the problematic Cheatgrass.⁷ If we can meet these challenges, then megafires may finally be extinguished.

References

1.  Why we have such large wildfires this summer. http://www.seattletimes.com/seattle-news/northwest/why-we-have-such-damaging-wildfires-this-summer/ (accessed Oct. 9, 2015).
2.  National Geographic: How Megafires Are Remaking American Forests. http://news.nationalgeographic.com/2015/08/150809-wildfires-forest-fires-climate-change-science/ (accessed Oct. 11, 2015)
3. Climate Central: The Age of Western Wildfires. http://www.climatecentral.org/news/report-the-age-of-western-wildfires-14873 (accessed Oct. 9, 2015)
4. Deadly forest fire leads to resurrection of endangered tree. http://blogs.scientificamerican.com/extinction-countdown/deadly-forest-fire-leads-to-resurrection-of-endangered-tree/ (accessed Oct. 9, 2015)
5. Rasker, thesolutionsjournal 2015, 55-62.
6. NPR: Why Forest-Killing Megafires Are The New Normal. http://www.npr.org/2012/08/23/159373770/the-new-normal-for-wildfires-forest-killing-megablazes (accessed Oct. 11, 2015)
7. Keeley, International Journal of Wildland Fire, 2007, 16, 96–106
8. Stephens, Frontiers in Ecology and the Environment 2014, 12, 115-122.
9. Climate Central: Study Ties Warming Temps to Uptick in Huge Wildfires. http://www.climatecentral.org/news/warming-huge-wildfire-outbreaks-19521 (accessed Oct. 21, 2015)