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Infrastructure systems—sometimes referred to as critical infrastructure or lifelines—provide services such as energy, water, sanitation, transportation, and communications that are essential for social and economic activities. Moreover, these systems typically serve large populations and comprise geographically extensive networks. They are also highly interdependent, so outages in one system such as electric power or telecommunications often affect other systems. As a consequence, when infrastructure systems are damaged in disasters, the ensuing losses are often substantial and disproportionately large. Collapse of a single major bridge, for example, can disrupt traffic flows over a broad region and impede emergency response, evacuation, commuting, freight movement, and economic recovery. Power outages in storms and other hazard events can affect millions of people, shut down businesses, and even cause fatalities. Infrastructure outages typically last from hours to weeks but can extend for months or even years. Minimizing disruptions to infrastructure services is thus key to enhancing communities’ disaster resilience. Research on infrastructure systems in natural hazards has been growing, especially as major disasters provide new data, insights, and urgency to the problem. Engineering advances have been made in understanding how hazard stresses may damage the physical components of infrastructure systems such as pipes and bridges, as well as how these elements can be designed to better withstand hazards. Modeling studies have assessed how physical damage disrupts the provision of services—for example, by indicating which neighborhoods in an urban area may be without potable water—and how disruption can be reduced through engineering and planning. The topic of infrastructure interdependencies has commanded substantial research interest. Alongside these developments, social science and interdisciplinary research has also been growing on the important topic of how infrastructure disruption in disasters has affected populations and economies. Insights into these impacts derive from a variety of information sources, including surveys, field observations, analysis of secondary data, and computational models. Such research has established the criticality of electric power and water services, for example, and the heightened vulnerability of certain population groups to infrastructure disruption. Omitting the socioeconomic impacts of infrastructure disruptions can lead to underinvestment in disaster mitigation. While the importance of understanding and reducing infrastructure disruption impacts is well-established, many important research gaps remain.

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Natural Hazard Science. Please check back later for the full article. Rock avalanches are very large (> 1 million cubic meters) landslides from rock slopes, which can travel much farther across the landscape than smaller events; the larger the avalanche, the greater the excess travel distance. Rock avalanches first became prominent in Switzerland in the 1800s, when the Elm and Goldau events killed people a surprisingly long way from the origin of the landslide; these events first posed the “long-runout rock-avalanche” problem. In essence, the long runout of these events appears to require low friction beneath and within the moving rock mass in order to explain their extremely long deposits; but in spite of recently intense research, this low friction still lacks a generally accepted explanation. Large collapses of volcano edifices can also generate rock avalanches that travel very long distances, albeit with a different runout-volume relationship to that of non-volcanic events. Compounding the puzzle is the presence of long-runout deposits not just on land, but also beneath the sea and on the surfaces of Mars and the Moon. Numerous studies of rock avalanches have yielded some consistencies of material and behavior, for example, that little or no mixing of material occurs within the moving debris mass during runout; that the deposit material beneath a meter-scale surface layer is pervasively and intensely fragmented, with fragments down to sub-micron size; that many of these fragments are themselves agglomerates of even finer particles; that throughout the travel of a rock avalanche, large volumes of fine dust are produced; that rock avalanche surfaces are typically hummocky at a range of scales; and that there are definite trends in plots of runout distance against volume from rock avalanches in different environments. Since rock avalanches can travel tens of kilometers from their source, they pose severe, if low-probability, direct hazards to societal assets in mountain valleys. Compounding this is their effect in the triggering of extensive and long-duration geomorphic hazard cascades. Although large rock avalanches are rare, magnitude-frequency studies show that the proportion of total volume involved in large events is greater than the proportion in small events, so that a large proportion of the total sediment generated in mountains by uplift and denudation originates in large rock avalanches. Consequently, large rock avalanches exert a significant influence on mountain geomorphology by, for example, blocking rivers and forming landslide dams; these either fail, causing large dambreak floods and intense, long-duration aggradation episodes to propagate down river systems; or remain intact to infill with sediment and form large valley flats. Rock avalanches that fall onto glaciers often result in large terminal moraines being formed as debris accumulates at the glacier terminus, and these moraines may have no relation to any climatic change. In addition, misinterpretation of rock avalanche deposits as moraines can cause serious underestimation of hazard risk and misinterpretation of paleoclimate; for example, a deposit 28 km long in Kyrgyzstan was originally thought to be of glacial origin, but it is now known to be a rock avalanche caused by coseismic failure of a mountain slope. Rock avalanche runout behavior poses truly fundamental scientific questions, and rock avalanches have important effects on a wide range of geomorphic processes. Better understanding of these awesome events is crucial for both geoscientific progress and for reducing impacts of future disasters.

Floods remain the most devastating natural hazard globally, despite substantial investments in flood prevention and management in recent decades. Fluvial floods, such as the ones in Pakistan in 2010 and Thailand in 2011, can affect entire countries and cause severe economic and human losses. Also, coastal floods can inflict substantial harm owing to their destructive forces in terms of wave and tidal energy. A flood type that received growing attention in recent years is flooding from pluvial events (heavy rainfall). Even though these are locally confined, their sudden onset and unpredictability pose a danger to areas that are generally not at risk from flooding. In the future, it is projected that flood risk will increase in many regions both because of the effects of global warming on the hydrological cycle and the continuing concentration of people and economic assets in risk-prone areas. Floods have a large variety of societal impacts that span across space and time. While some of these impacts are obvious and have been well researched, others are more subtle and less is known about their complex processes and long-term effects. The most immediate and apparent impact of floods is direct damage caused by physical contact between floodwaters and economic assets, cultural heritage, or human beings, with the result for humans being injuries and deaths. Direct flood damage can amount to billions of US dollars for single events, such as the floods in the Danube and Elbe catchment in Central Europe in 2002 and 2013. More indirect economic implications are the losses that occur outside of the flood event in space and time, such as losses due to business disruption. The flood in Thailand in 2011, for instance, resulted in a lack of auto parts supplies and consequently the shutdown of car manufacturing within and outside the flood zone. Floods also have long-term indirect impacts on flood-affected people and communities. Experiencing property damage and losing important personal belongings can have a negative psychological effect on flood victims. Much less is known about this type of flood impact: how long do these impacts last? What makes some people or communities recover faster than others from financial losses and emotional stress? Moreover, flood impacts are not equally distributed across different groups of society. Often, poor, elderly, and marginalized societal groups are particularly vulnerable to the effects of flooding inasmuch as these groups generally have little social, human, and financial coping capacities. In many countries, women regularly bear a disproportionately high burden because of their societal status. Finally, severe floods often provide so-called windows of opportunities, enabling rapid policy change, resulting in new flood risk management policies. Such newly adopted policy arrangements can lead to societal conflicts over issues of interests, equity, and fairness. For instance, flood events often trigger large-scale investment in flood defense infrastructure, which are associated with high construction costs. Although these costs are usually borne by the taxpayer, often only a small proportion of society shares in their benefits. In addition, societal conflict can arise concerning where to build structural measures; what impacts these measures have on the ground regarding economic development potentials, different kinds of uses, and nature protection; and which effects are expected downstream. In such controversies, issues of participation and decision making are central and often highly contested. While floods are usually associated with negative societal impacts in industrialized countries, they also have beneficial impacts on nature and society. In many parts of the world, the livelihood of millions of people depends on the recurring occurrence of flooding. For instance, farming communities in or near floodplains rely upon regular floodwaters that carry nutrients and sediments, enriching the soil and making it fertile for cultivation.