🌋Natural and Human Disasters Unit 2 – Geological Hazards

Key Concepts and Definitions

• Geological hazards refer to naturally occurring events or processes that originate from the Earth's surface or interior and have the potential to cause harm or damage to humans, infrastructure, and the environment
• Vulnerability describes the susceptibility of a population, structure, or area to the adverse effects of a hazard, influenced by factors such as location, construction quality, and socioeconomic conditions
• Risk is the probability of a hazard occurring combined with the potential consequences or impacts, often expressed as a product of hazard, exposure, and vulnerability
• Resilience refers to the ability of a system, community, or society to resist, absorb, accommodate, adapt to, transform, and recover from the effects of a hazard in a timely and efficient manner
• Mitigation encompasses the actions taken to reduce or minimize the adverse impacts of a hazard before, during, or after its occurrence, aiming to lessen vulnerability and increase resilience
• Preparedness involves the knowledge, capabilities, and actions developed by governments, organizations, communities, and individuals to effectively anticipate, respond to, and recover from the impacts of likely, imminent, or current hazard events or conditions
• Early warning systems are integrated systems that monitor, collect, and analyze data on potential hazards, provide timely and accurate information to authorities and the public, and trigger appropriate responses to minimize harm

Types of Geological Hazards

• Earthquakes are sudden and violent shaking of the ground caused by the release of energy from the Earth's crust, often along fault lines, and can cause significant damage to buildings and infrastructure
• Volcanic eruptions occur when magma, gases, and ash escape from a volcano, potentially leading to lava flows, pyroclastic density currents, ash fall, and other hazards that can impact nearby communities and disrupt air travel
• Landslides are the downslope movement of soil, rock, or debris under the influence of gravity, often triggered by heavy rainfall, earthquakes, or human activities such as deforestation and construction
• Tsunamis are large, powerful waves generated by underwater disturbances such as earthquakes, volcanic eruptions, or submarine landslides that can inundate coastal areas and cause widespread damage and loss of life
• Sinkholes are depressions or holes that form when the surface layer of the ground collapses due to the dissolution of underlying rock (karst) or the extraction of groundwater, oil, or gas
• Soil liquefaction occurs when water-saturated soil loses strength and stiffness in response to applied stress, such as during an earthquake, causing the soil to behave like a liquid and potentially leading to foundation failures and structural damage
• Coastal erosion is the gradual wearing away of land and beaches by waves, currents, tides, and wind, which can be exacerbated by human activities (coastal development) and sea-level rise, leading to the loss of property and infrastructure

Causes and Mechanisms

• Plate tectonics drive many geological hazards, as the movement and interaction of the Earth's lithospheric plates can lead to earthquakes, volcanic eruptions, and tsunamis
  • Convergent boundaries, where plates collide, are associated with subduction zones, deep-focus earthquakes, and the formation of volcanic arcs
  • Divergent boundaries, where plates move apart, are characterized by shallow earthquakes, rift valleys, and submarine volcanic eruptions along mid-ocean ridges
  • Transform boundaries, where plates slide past each other, are prone to shallow, strike-slip earthquakes and can produce significant ground motion
• Volcanic eruptions are caused by the ascent and extrusion of magma from the Earth's interior, driven by buoyancy and gas pressure
  • Magma composition (silica content) and gas content influence the explosivity of eruptions, with more silicic and gas-rich magmas leading to more explosive events
  • Eruption styles range from effusive (lava flows) to explosive (pyroclastic density currents and ash fall), depending on magma properties and vent conditions
• Landslides can be triggered by various factors, including intense rainfall, earthquakes, volcanic activity, and human-induced changes to the landscape
  • Slope stability is influenced by factors such as rock and soil type, slope angle, vegetation cover, and the presence of water, with unconsolidated materials and steep slopes being more susceptible to failure
• Sinkholes form through two main processes: the gradual dissolution of soluble bedrock (usually limestone or dolomite) by groundwater, or the sudden collapse of overlying material into pre-existing voids or cavities
• Coastal erosion is driven by the combined effects of waves, currents, tides, and wind, which can be influenced by factors such as sea-level rise, storm intensity and frequency, and human modifications to the shoreline (e.g., the construction of seawalls or groins)

Detection and Monitoring

• Seismometers and seismic networks are used to detect and record earthquakes, providing information on their location, magnitude, and depth, which can help in understanding fault systems and assessing seismic hazards
• Volcano monitoring involves a combination of techniques, including seismic monitoring (detecting volcanic tremors and earthquakes), ground deformation measurements (using GPS and satellite radar interferometry), and gas emission analysis (monitoring changes in the composition and flux of volcanic gases)
• Landslide monitoring can involve the use of remote sensing techniques (satellite imagery and LiDAR), ground-based instruments (inclinometers, extensometers, and piezometers), and field observations to detect and track the movement of slopes and identify potential failure zones
• Tsunami detection relies on a network of deep-ocean buoys and coastal tide gauges that measure changes in sea level and can provide early warnings to coastal communities
• Sinkhole monitoring can involve the use of ground-penetrating radar (GPR), electrical resistivity surveys, and borehole cameras to identify and characterize subsurface voids and cavities
• Coastal erosion monitoring employs techniques such as beach profiling, LiDAR surveys, and satellite imagery analysis to track changes in shoreline position and beach morphology over time
• Crowdsourcing and citizen science initiatives can supplement official monitoring efforts by engaging the public in reporting observations and collecting data on geological hazards, such as through smartphone apps or online platforms

Impact on Humans and Environment

• Earthquakes can cause widespread damage to buildings, infrastructure, and lifelines (transportation networks, power grids, and water systems), leading to significant economic losses and disruption of essential services
  • Strong ground motion can lead to structural failures, especially in poorly designed or constructed buildings, and can trigger secondary hazards such as landslides, liquefaction, and fires
  • Earthquakes can also result in human casualties, particularly in densely populated areas with vulnerable building stock, and can have long-lasting psychological impacts on affected communities
• Volcanic eruptions can have far-reaching consequences, affecting local communities, regional economies, and global climate
  • Lava flows, pyroclastic density currents, and ash fall can cause direct damage to buildings, infrastructure, and agricultural land, while volcanic gases and acid rain can impact air and water quality
  • Volcanic ash can disrupt air travel, damage aircraft engines, and cause respiratory health problems, while large-scale eruptions can influence global climate by injecting sulfur dioxide into the stratosphere, leading to temporary cooling
• Landslides can cause damage to buildings, roads, and utilities, and can lead to the loss of life, particularly in populated areas with limited evacuation routes
  • Landslides can also have significant environmental impacts, such as altering drainage patterns, increasing sediment loads in rivers and streams, and destroying habitats
• Tsunamis can cause massive destruction along coastal areas, leading to the loss of life, damage to buildings and infrastructure, and long-term economic and social disruption
  • The inundation of low-lying areas can result in drowning, injuries, and the displacement of large numbers of people, while the force of the waves can cause structural damage and erosion
• Sinkholes can cause localized damage to buildings, roads, and other infrastructure, and can pose a risk to public safety
  • The collapse of sinkholes can also lead to the contamination of groundwater resources and the alteration of surface drainage patterns
• Coastal erosion can lead to the loss of beaches, dunes, and coastal habitats, as well as damage to coastal properties and infrastructure
  • The loss of natural coastal defenses can increase the vulnerability of coastal communities to flooding and storm surge, while the need for coastal protection measures can have significant economic and environmental costs

Risk Assessment and Mapping

• Hazard assessment involves identifying the potential geological hazards in a given area, characterizing their frequency, magnitude, and spatial extent, and evaluating the likelihood of their occurrence
  • This process often involves the analysis of historical records, geological and geomorphological mapping, and the use of probabilistic models to estimate the probability of future events
• Exposure assessment focuses on identifying the elements at risk, such as populations, buildings, and infrastructure, that could be affected by a given hazard
  • This involves the collection and analysis of data on the location, characteristics, and value of exposed assets, often using geographic information systems (GIS) and remote sensing techniques
• Vulnerability assessment evaluates the potential impact of a hazard on the exposed elements, considering factors such as the physical vulnerability of buildings and infrastructure, the social vulnerability of populations, and the capacity of communities to cope with and recover from the effects of a hazard
• Risk assessment combines information from hazard, exposure, and vulnerability assessments to estimate the potential consequences of a hazard event, often expressed in terms of economic losses, casualties, or other impact metrics
  • Quantitative risk assessment methods, such as probabilistic risk analysis, can provide a more rigorous and systematic approach to estimating risk, while qualitative methods, such as risk matrices, can be useful for risk prioritization and communication
• Risk mapping involves the spatial representation of hazard, exposure, vulnerability, and risk information, typically using GIS to produce maps that can support decision-making and risk communication
  • Hazard maps depict the spatial distribution and intensity of potential hazards, while exposure maps show the location and characteristics of elements at risk
  • Vulnerability maps illustrate the spatial variation in the susceptibility of exposed elements to the effects of a hazard, while risk maps combine hazard, exposure, and vulnerability information to provide a comprehensive view of risk

Mitigation Strategies

• Land-use planning and zoning regulations can be used to guide development away from hazard-prone areas and to ensure that new construction meets appropriate design and building standards
  • This can involve the creation of hazard zones, the establishment of setback lines or buffer zones, and the use of incentives or disincentives to encourage risk-sensitive development
• Building codes and retrofitting standards can be implemented to improve the resilience of buildings and infrastructure to geological hazards
  • This can include requirements for seismic-resistant design, the use of fire-resistant materials in volcanic areas, and the elevation of structures in flood-prone areas
  • Retrofitting existing buildings can involve structural modifications, such as the addition of shear walls or the strengthening of foundations, to improve their performance during hazard events
• Nature-based solutions, such as the preservation or restoration of natural features (wetlands, dunes, and mangroves), can provide a cost-effective and sustainable approach to mitigating the impacts of geological hazards
  • These solutions can help to attenuate the effects of hazards, such as reducing wave energy during tsunamis or stabilizing slopes prone to landslides, while also providing co-benefits such as habitat creation and carbon sequestration
• Early warning systems can be developed to provide timely and accurate information to authorities and the public about impending hazard events, allowing for the implementation of emergency response and evacuation plans
  • These systems typically involve the integration of monitoring networks, data analysis and modeling tools, and communication channels, and require effective coordination between scientific agencies, government authorities, and local communities
• Public education and awareness programs can be implemented to improve the understanding of geological hazards and to promote risk-reducing behaviors among individuals and communities
  • This can include the development of educational materials, the organization of workshops and training sessions, and the use of media campaigns and participatory approaches to engage the public in hazard preparedness and mitigation efforts
• Insurance and risk transfer mechanisms can be used to manage the financial impacts of geological hazards and to incentivize risk reduction measures
  • This can include the provision of hazard insurance to homeowners and businesses, the establishment of catastrophe bonds or other risk transfer instruments, and the use of risk-based pricing to encourage the adoption of mitigation measures

Case Studies and Historical Events

• The 1906 San Francisco earthquake (magnitude 7.8) caused extensive damage to the city, triggering fires that burned for several days and leading to the deaths of over 3,000 people, highlighting the importance of seismic-resistant building design and emergency response planning
• The eruption of Mount Vesuvius in 79 AD buried the Roman cities of Pompeii and Herculaneum under ash and pyroclastic flows, preserving a unique record of Roman life and providing insights into the devastating impacts of volcanic eruptions on ancient societies
• The 1970 Huascarán debris avalanche in Peru, triggered by a massive earthquake, resulted in the deaths of over 20,000 people and the destruction of several towns, underscoring the cascading effects of geological hazards and the vulnerability of mountain communities
• The 2004 Indian Ocean tsunami, generated by a magnitude 9.1 earthquake off the coast of Sumatra, caused widespread destruction and loss of life across 14 countries, leading to increased efforts to develop and improve tsunami early warning systems and coastal resilience
• The formation of the Bayou Corne sinkhole in Louisiana, USA, in 2012, caused by the collapse of a salt dome cavern used for oil and gas storage, led to the evacuation of nearby residents and highlighted the risks associated with human activities in karst environments
• The ongoing coastal erosion and sea-level rise affecting the Maldives, a low-lying island nation in the Indian Ocean, poses a significant threat to the country's economy, infrastructure, and habitability, prompting the government to explore adaptation strategies such as coastal protection and planned relocation
• The 2011 Tōhoku earthquake and tsunami in Japan (magnitude 9.0) caused widespread damage to coastal communities, triggered a nuclear accident at the Fukushima Daiichi power plant, and led to increased investment in disaster risk reduction and resilience-building measures across the country
• The 1999 Vargas tragedy in Venezuela, where heavy rainfall triggered thousands of landslides and debris flows, resulted in the deaths of tens of thousands of people and the destruction of coastal communities, highlighting the need for improved land-use planning and early warning systems in landslide-prone areas