Lecture 3 - Volcano hazards Flashcards
What kind of hazard is a volcano?
Geological
- Earthquake
- Volcano
- Mass movement
- Rockfall, landslide, avalanche, subsidence
How many Holocene volcanoes are listed in the VOTW database, and where are they concentrated?
1,500 volcanoes are listed in the VOTW database, with most eruptions concentrated along the Pacific Ring of Fire, Indonesia, Japan, Iceland, and Central America.
Which tectonic settings are most associated with Holocene eruptions?
Most Holocene eruptions occur at convergent plate boundaries, especially subduction zones, as well as along mid-ocean ridges like the Mid-Atlantic Ridge
What are some notable regions and statistics for Holocene eruptions?
75% of eruptions occur along the Pacific Ring of Fire, with Indonesia having the most Holocene volcanoes. Additionally, 70% of volcanic activity happens underwater, but only a small fraction is documented
How many people globally live within 100 km of an active volcano?
Over 800 million people live within 100 km of an active volcano, placing them at potential risk from volcanic hazards.
Which regions have the highest populations living near volcanoes?
The highest populations are concentrated in Southeast Asia (Indonesia, Philippines), Japan, Central America, and parts of the Mediterranean.
Why are so many people living near volcanoes?
Many people live near volcanoes due to the fertile soils that are suitable for agriculture, economic opportunities, and historical settlement patterns despite the volcanic risks.
What is a divergent boundary?
A divergent boundary is where tectonic plates move away from each other, creating new crust. Examples include mid-ocean ridges like the Mid-Atlantic Ridge and continental rifts like the East African Rift.
What is a convergent boundary?
A convergent boundary is where tectonic plates move toward each other, often causing subduction. Examples include the Andes Mountains (oceanic-continental) and the Himalayas (continental-continental).
What is a transform boundary?
A transform boundary is where tectonic plates slide horizontally past each other. Examples include the San Andreas Fault in California and the Alpine Fault in New Zealand.
How does basaltic magma composition affect volcanic hazards?
Basaltic magma is low in silica, making it low-viscosity and allowing lava to flow easily. This creates hazards like lava flows and fire fountains, which are less explosive but can cover large areas (e.g., Hawaiian eruptions).
How does andesitic magma composition influence volcanic hazards?
Andesitic magma has moderate silica content, leading to higher viscosity and more explosive eruptions. Hazards include pyroclastic flows, ashfall, and lava domes, commonly seen in stratovolcanoes (e.g., Mount St. Helens).
What hazards are associated with rhyolitic magma?
Rhyolitic magma is high in silica, making it very viscous and prone to violent explosions. It can generate dangerous hazards such as large pyroclastic flows, volcanic ash clouds, and caldera formation (e.g., Yellowstone).
What are the characteristics and hazards of a composite volcano (stratovolcano)?
Composite volcanoes are large, steep-sided cones formed from layers of lava and ash. They are associated with explosive eruptions due to viscous magma (often andesitic or rhyolitic). Hazards include pyroclastic flows, ashfall, lava domes, and lahars (e.g., Mount Vesuvius)
What are the characteristics and hazards of a shield volcano?
Shield volcanoes have broad, gently sloping sides, formed from low-viscosity basaltic lava that flows easily. Hazards include extensive lava flows that can cover vast areas, though eruptions are typically non-explosive (e.g., Mauna Loa, Hawaii).
What are the characteristics and hazards of a cinder cone volcano?
Cinder cones are small, steep-sided volcanoes made from volcanic fragments like ash and cinders. Eruptions are usually short-lived, producing lava fountains, ash, and lapilli. While smaller in size, their eruptions can still pose hazards to nearby areas (e.g., Parícutin, Mexico)
What are the characteristics and hazards of a fissure volcano?
Fissure volcanoes form along cracks in the Earth’s crust, from which basaltic lava flows out. They produce extensive lava flows, covering large areas, but lack a central cone. Hazards include widespread lava inundation (e.g., the Laki fissure in Iceland).
What are the characteristics and hazards of a lava dome volcano?
Lava domes are formed by the slow extrusion of viscous lava (often rhyolitic or andesitic), creating steep-sided mounds. Hazards include dome collapse, leading to pyroclastic flows, and explosive eruptions if gas pressure builds (e.g., Mount St. Helens lava dome).
What are the characteristics and hazards of a caldera volcano?
Calderas form when a volcano’s summit collapses following a large explosive eruption. Hazards include massive pyroclastic flows, ashfall, and long-term hazards from residual volcanic activity. Calderas can be enormous, with eruptions causing widespread devastation (e.g., Yellowstone Caldera).
What is the Hawaiian eruption style?
The Hawaiian eruption style is characterized by non-explosive, relatively gentle eruptions where basaltic lava flows easily from vents or fissures, creating broad, shield-shaped volcanoes (e.g., Mauna Loa, Kīlauea).
What are the main volcanic hazards associated with Hawaiian eruptions?
The main hazards include lava flows, which can cover large areas, destroy infrastructure, and ignite fires, and lava fountains, which shoot molten lava into the air, though they pose less risk to life compared to explosive eruptions.
How does magma composition affect Hawaiian eruptions?
Hawaiian eruptions involve basaltic magma, which has low silica content, making it low-viscosity and allowing lava to flow easily, resulting in slow-moving lava flows rather than explosive eruptions
What are Strombolian eruptions characterized by?
Strombolian eruptions are characterized by intermittent bursts of lava and explosive activity, producing lava fountains and small pyroclastic flows.
What type of magma is associated with Strombolian eruptions, and what are the hazards?
Strombolian eruptions typically involve basaltic or andesitic magma, leading to hazards like lava fountains, pyroclastic flows, ashfall, and ballistic projectiles.
Where are Strombolian eruptions commonly found, and how do they differ from Hawaiian eruptions?
Commonly found in subduction zones, such as Stromboli Island in Italy, they differ from Hawaiian eruptions by having more episodic and explosive activity rather than continuous lava flow.
What are Vulcanian eruptions characterized by?
Vulcanian eruptions are characterized by short, violent explosions of thick, viscous magma that result in ash clouds, pyroclastic flows, and the ejection of volcanic rock fragments.
What type of magma is associated with Vulcanian eruptions, and what are the typical hazards?
Vulcanian eruptions are associated with andesitic or rhyolitic magma, leading to hazards such as ashfall, pyroclastic flows, and ballistic projectiles, which can pose serious risks to nearby populations.
Where are Vulcanian eruptions commonly found?
Commonly found in stratovolcanoes (e.g., Vulcano in Italy)
What are Sub-Plinian eruptions characterized by, and what is an example?
Sub-Plinian eruptions involve paroxysmal ejection and wide dispersal of tephra (including pumice), sometimes associated with pyroclastic surges. An example is the Vesuvius eruption in Italy, 1631.
What defines Plinian eruptions, and what is a notable historical example?
Plinian eruptions are marked by paroxysmal ejection and wide dispersal of tephra (including pumice), often linked to caldera collapse. A notable example is the Vesuvius eruption in AD 79.
What characterizes Ultra-Plinian eruptions, and can you provide an example?
Ultra-Plinian eruptions feature paroxysmal ejection and wide dispersal of tephra (including pumice), often resulting in caldera collapse and formation of ash plumes. An example is the Tambora eruption in Indonesia, 1815.
What is magnitude in the context of volcanic eruptions, and how is it calculated?
Magnitude measures the size of an eruption based on a logarithmic index of erupted mass, defined as:
Magnitude = log10 (erupted mass in kg) - 7.
How is intensity defined in relation to volcanic eruptions?
Intensity measures the eruption rate and is calculated as:
Intensity = log10 (mass eruption rate in kg/s) + 3.
What is the Volcanic Explosivity Index (VEI)?
The Volcanic Explosivity Index (VEI) is a scale that categorizes eruptions based on their magnitude and intensity, allowing for a comparison of eruption sizes and impacts.
What are the two main types of volcanic hazards?
The two main types are direct hazards (events produced during or shortly after an eruption) and indirect hazards (destructive processes incidental to eruptions).
What are examples of direct hazards associated with volcanic eruptions?
- Ballistics (ejected lava/rock fragments)
- Ash and tephra fall (airborne volcanic material)
- Lava flows (molten rock flow)
- Pyroclastic falls, flows, and surges (hot volcanic materials)
- Gases (volatile compounds released)
What are ballistics in the context of volcanic eruptions?
Ballistics are fragments of lava (bombs) or rock (blocks) ejected during explosive eruptions. They can range from a few centimetres to tens of meters in diameter and can travel up to ~10 km from the vent
How do ash and tephra fall occur during volcanic eruptions?
Tephra consists of fragments of rock and lava of any size that become airborne during an eruption. Volcanic ash is specifically tephra <2 mm in diameter, carried downwind and falling out of suspension.
What are the characteristics of lava flows?
Lava flows are the most common hazard from non-explosive eruptions, typically moving slowly (a few meters to several kilometers per hour). The distance they travel depends on their viscosity, effusion rate, and the surrounding topography.
