Geophysical hazards Flashcards
What are geophysical hazards and what processes do they encompass?
Geophysical hazards refer to natural events resulting from the Earth’s internal processes. These include earthquakes, volcanic eruptions, and mass movements such as landslides, rockslides, debris flows, and mudflows. These hazards can have devastating impacts on human life, infrastructure, and the environment.
Describe the eruption of Mount Marapi on December 3, 2023. What were its effects?
On December 3, 2023, Mount Marapi erupted on the Indonesian island of Sumatra, producing an ash plume that reached heights of 3,000 meters. The eruption deposited significant amounts of volcanic ash in surrounding districts, leading to the tragic death of twenty-three hikers found near the volcano’s crater. This event highlights the dangers associated with volcanic activity in populated areas.
What are the three types of tectonic plate boundaries and their associated geological activities?
- Converging Boundaries: Tectonic plates move towards each other (→ ←), causing intense geological activity such as earthquakes and volcanic eruptions due to subduction or collision.
- Divergent Boundaries: Plates move apart (← →), leading to the formation of new crust through volcanic activity and frequent earthquakes as magma rises to fill the gap.
- Transform Boundaries: Plates slide past each other horizontally (↔), primarily resulting in earthquakes without significant volcanic activity.
What recent seismic activity has been observed in Iceland and its implications?
Since October 24, 2023, Iceland has experienced a series of earthquakes on the Reykjanes peninsula, indicating a high probability of an impending volcanic eruption. Evacuations have occurred in anticipation of potential hazards. The Fagradalsfjall volcano has erupted three times since 2021, creating new landscapes known as cooling craters.
Explain the structure of the Earth and its geological history.
The Earth’s structure consists of four main layers: the crust, mantle, outer core, and inner core. The crust, the outermost layer, is a solid rocky shell ranging from 5 to 70 kilometers in depth, with oceanic crust being thinner and denser than continental crust. Beneath the crust lies the mantle, a semi-solid layer approximately 2,900 kilometers thick, composed primarily of iron, magnesium, and silicon-rich rocks. The outer core is a liquid layer of iron and nickel, approximately 2,260 kilometers thick, which generates Earth’s magnetic field. At the center is the inner core, a solid sphere of iron and nickel with temperatures reaching 5,000-6,000°C. These layers are differentiated by their physical and chemical properties, with boundaries discovered through seismic observation
What types of volcanoes exist and what are their characteristics?
- Shield Volcanoes: Broad and gently sloping; formed by low-viscosity basaltic lava that flows easily over great distances (e.g., Mauna Loa in Hawaii).
- Composite Volcanoes (Stratovolcanoes): Steep-sided and characterized by alternating layers of lava flows and ash; often associated with explosive eruptions (e.g., Mount St. Helens).
- Cinder Cone Volcanoes: Smallest type; built from ejected lava fragments that solidify before falling to the ground; typically have steep slopes (e.g., Paricutin in Mexico).
What are primary and secondary hazards associated with volcanic eruptions?
Primary hazards include:
- Lava Flows: Molten rock that erupts from a volcano; can destroy everything in its path but moves slowly enough for evacuation in many cases.
- Ash Fall: Volcanic ash can travel hundreds of kilometers from the eruption site, causing respiratory issues for humans and animals, damaging crops, and collapsing roofs.
- Volcanic Gases: Emissions such as carbon dioxide and sulfur dioxide can be hazardous to health and contribute to climate change.
Secondary hazards include:
- Lahars: Mudflows formed when volcanic ash mixes with water from rainfall or melting snow; they can travel rapidly down river valleys.
- Rock Avalanches: Occur when volcanic structures collapse due to instability; can cause significant destruction.
Describe different types of magma and their implications for volcanic eruptions.
- Basaltic Magma: Forms at constructive boundaries; low viscosity allows for fluid lava flows; results in less explosive eruptions.
- Andesitic Magma: Intermediate silica content leads to moderate viscosity; can cause explosive eruptions.
- Rhyolitic Magma: High silica content results in high viscosity; often leads to highly explosive eruptions due to trapped gases.
Magma composition influences eruption style: basaltic eruptions tend to be less violent compared to rhyolitic eruptions.
What is liquefaction during an earthquake? Provide an example.
Liquefaction occurs when saturated soil loses its strength due to shaking during an earthquake, behaving like a liquid rather than solid ground. This phenomenon can lead to buildings sinking or tilting dangerously. A notable example is the Christchurch earthquake on February 22, 2011, where liquefaction caused extensive damage to infrastructure.
How do human activities contribute to geophysical hazards? List specific activities and their impacts.
Human activities such as mining disturb geological structures, while dam construction adds weight to faults that may trigger seismic events. Fracking increases seismicity by injecting high-pressure fluids into rock formations, altering stress levels in faults. Urbanization can also lead to increased runoff and erosion that destabilizes slopes.
What are the characteristics and impacts of lava flows as a primary volcanic hazard? Provide an example.
Lava flows are molten rock that erupts from a volcano and can travel several kilometers from the vent, depending on the viscosity of the magma. Basaltic lava flows are typically less viscous and can move at speeds up to 40 km/h. While they can destroy buildings and infrastructure, they usually move slowly enough to allow for evacuation. A significant example occurred during the 2014-2015 eruption of Kilauea in Hawaii, where lava flows threatened the town of Pahoa, causing evacuations and property damage
Describe pyroclastic flows and their associated risks. Include a historical example.
Pyroclastic flows are fast-moving currents of hot gas, ash, and volcanic rock that can reach speeds of up to 700 km/h and temperatures exceeding 600 °C. They are among the deadliest volcanic hazards due to their speed and density, capable of incinerating everything in their path. On June 3, 2018, Guatemala’s Volcán de Fuego produced a violent eruption that generated pyroclastic density currents (fast-moving mixtures of ash, gas, and volcanic debris). These flows buried entire villages, including San Miguel Los Lotes and El Rodeo, under meters of volcanic material, killing at least 437 people
What are the effects of ash fall as a primary volcanic hazard? Provide an example of its impact.
Ash fall consists of fine particles ejected during an eruption that can blanket large areas, leading to respiratory issues, damage to crops, and structural collapse due to weight accumulation on roofs. The 2010 eruption of Eyjafjallajökull in Iceland produced an ash cloud that disrupted air travel across Europe for several weeks, affecting millions and causing significant economic losses.
Explain volcanic gas emissions as a primary hazard and provide a notable incident.
Volcanic gases such as carbon dioxide, sulfur dioxide, and hydrogen sulfide can be released during eruptions, posing health risks to humans and animals. In extreme concentrations, these gases can lead to fatalities. A tragic incident occurred at Lake Nyos in Cameroon in 1986 when a sudden release of carbon dioxide from the lake suffocated approximately 1,700 people and thousands of livestock in nearby villages.
What are lahars, how do they form, and what is a significant example?
Lahars are volcanic mudflows created when volcanic ash mixes with water from rainfall or melting snow/ice. They can flow rapidly down river valleys, causing destruction far from the volcano. During the June 2024 eruption of Kanlaon in the Philippines, heavy rainfall triggered lahars in La Castellana, carrying volcanic debris, tree trunks, and large boulders downslope, damaging communities and infrastructure.
Describe jökulhlaups and their consequences with an example.
Jökulhlaups are glacial outburst floods that occur when volcanic eruptions beneath glaciers melt large volumes of ice rapidly. These floods can sweep away everything in their path. A notable instance was during the 2010 Eyjafjallajökull eruption in Iceland when melting ice caused jökulhlaups that destroyed roads and bridges.
What is acid rain resulting from volcanic eruptions? Provide an example of its effects.
Acid rain forms when sulfur dioxide emitted during an eruption reacts with water vapor in the atmosphere to create sulfuric acid. This can damage crops, forests, aquatic ecosystems, and infrastructure. An example is the acid rain resulting from the eruption of Mount St. Helens in Washington State in 1980, which adversely affected local agriculture and water quality.
How do landslides relate to volcanic activity? Provide a historical case study.
Landslides can occur due to volcanic activity when unstable slopes fail under the weight of accumulated ash or during explosive eruptions. They can also transform into lahars if water is involved. On February 17, 2006, a catastrophic rock slide-debris avalanche occurred in Southern Leyte, Philippines, burying the village of Guinsaugon and killing over 1,100 people. The disaster involved 15-20 million cubic meters of debris that traveled 3.8 km at high velocity, flattening everything in its path.
What is the significance of the Earth’s crust and its relationship to human habitation?
The Earth’s crust is the outermost layer where humans live, and its thickness is comparable to that of a piece of paper relative to the entire planet. Beneath the crust lies the molten mantle, which cannot be accessed by humans due to extreme temperatures that would incinerate any material. The crust’s stability is crucial for human settlements, as geological processes beneath can lead to hazards like earthquakes and volcanic eruptions.
How does the movement of tectonic plates drive geological changes?
The movement of tectonic plates, driven by superheated magma from the mantle, causes shifts in land masses over geological time. Approximately 220 million years ago, these movements shaped the current configuration of continents. Evidence of this movement is seen in similar fossil records across different continents, indicating that they were once connected.
What types of seismic waves are generated during an earthquake? Describe their characteristics.x
- Primary Waves (P-waves): Fastest seismic waves, traveling through solids and fluids; characterized by alternating compressions and dilations.
- Secondary Waves (S-waves): Slower than P-waves, only travel through solids; involve transverse motion perpendicular to wave direction.
- Love Waves: Surface waves causing horizontal shaking; largest amplitude at the surface.
- Rayleigh Waves: Cause elliptical rolling motion similar to ocean waves; penetrate deeper but have lower speed than Love waves.
What factors increase a slope’s susceptibility to mass movement?
Several factors contribute to slope instability:
- Water: Increases weight and acts as a lubricant for materials.
- Erosion Processes: Coastal or river erosion can weaken slopes.
- Gradient of Slope: Steeper slopes are more prone to failure.
- Rock Type: Soft rocks like mudstone are more susceptible than hard rocks like limestone.
- Vegetation Removal: Lack of vegetation reduces soil stability as roots help anchor sediments.
How do human activities contribute to geophysical hazards? Provide specific examples.
Human activities such as mining can destabilize geological structures, while urbanization alters natural drainage patterns, increasing flood risks. For instance, dam construction adds significant weight to fault lines, potentially triggering earthquakes. Fracking has been linked to increased seismic activity due to high-pressure fluid injections into rock formations.
How does water influence slope stability and contribute to mass movement?
Water adds weight to the materials on a slope, increasing the overall load and reducing the frictional resistance that holds the slope together. When water saturates the soil, it can lead to a significant decrease in shear strength, making it easier for materials to slide downwards. Additionally, water can create hydrostatic pressure within soil layers, which destabilizes them further. For example, heavy rainfall can trigger landslides by saturating the ground, as seen during intense storms in regions like California.