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1. Tectonic disaster risk
a) is the interaction between tectonic hazards, and vulnerability and exposure to earthquakes and volcanic eruptions
b) results in potential loss of human lives and damage to properties
2. Factors influencing disaster risks caused by earthquakes
a) nature of hazards including duration and time of shaking
b) vulnerable conditions including quality of building design and construction, and soil and rock properties; and exposure including population density and distance from epicentre
3. Factors influencing disaster risks caused by volcanic eruptions
a) nature of hazards including chemical composition of magma
b) vulnerable conditions including availability of surface and ground water in the development of lahars, prevailing wind conditions affecting direction and distribution of tephra; and exposure including presence of human settlements
Nature of tectonic hazards: The occurrences of tectonic hazards such as earthquakes and volcanic eruptions would increase the tectonic disaster risk. As each hazard is different from the other, the nature or characteristics of these hazards such as the duration of the hazardous event (i.e. shorter-term or longer-term events) are also important in determining the tectonic disaster risks.
Vulnerability: the conditions that increase the likelihood of a community and their properties being affected by hazards. These conditions include:
A community’s access to water, food, and health resources
A natural system’s likelihood to extreme weather and environmental degradation
Exposure: the extent to which people and properties are exposed to tectonic hazard areas, including the proximity of the community to a fault zone or active volcano
How does the nature of the earthquake and vulnerable conditions such as poor building design affect the disaster risk in the Turkey-Syria earthquake Feb 2023?
Watch the video below to find out more.
Watch th video below to see how soft soil led to liquefaction in an earthquake which struck Palu, Indonesia, causing greater risks and damages to the people in September 2018.
Watch the video on how the landslides from the earthquake on steep terrain hamper search and rescue in Taiwan after the 7.4 magnitude earthquake on 3 April 2024.
Let's compare the earthquakes which struck Haiti in 2010 and 2021. Why was the extent of damage greater in the 2010 earthquake though its magnitude is lower?
Watch the video on the volcanic eruption in Iceland. How do vulnerability, exposure and nature of the eruption affects the level of disaster risk in Iceland?
2025 volcanic eruption in Iceland.
Semeru erupted on 4 Dec 2021, a cloud of volcanic ash 12,000 m (40,000 ft) was ejected into the air, killing at least 57 people and injuring more than 100 others.
Why are the people living near Semeru volcano facing higher disaster risks?
In 2018, the eruption of Krakatoa triggered a tsunami that killed at least 420 people and injured 14,000 others.[
As a result of the landslide, the height of the volcano was reduced from 338 meters to 110 meters.
Factors influencing disaster risks caused by volcanic eruptions
The chemical composition of magma is a major factor influencing disaster risks.
The chemical composition of magma determines its viscosity, which in turn affects the type and explosiveness of volcanic eruptions.
Silica-rich magma (felsic magma) is more viscous and traps gases, leading to explosive eruptions that produce pyroclastic flows, ash clouds, and tephra. These can cause widespread destruction and fatalities.
For example, Mount Pinatubo (Philippines, 1991) erupted explosively due to its high silica and gas content, producing massive ash clouds that spread over 400 km, collapsing roofs and killing over 800 people.
In contrast, basaltic magma (low silica content) is less viscous, allowing gases to escape easily. This results in gentle effusive eruptions that produce lava flows, which are less deadly.
For instance, Mount Kilauea (Hawaii) erupts frequently but with fluid basaltic lava that moves slowly, giving residents time to evacuate — thus posing lower disaster risk.
Vulnerable conditions and exposure also affect disaster risks
Availability of surface and groundwater can greatly increase risks through the formation of lahars (volcanic mudflows).
After the 1991 eruption of Mount Pinatubo, heavy rainfall mixed with volcanic ash to create destructive lahars that buried villages and farmlands years after the eruption, affecting thousands of people.
This shows that secondary hazards linked to local conditions can sometimes be more damaging than the initial eruption itself.
Prevailing wind conditions influence the direction and distribution of tephra and ash, determining which areas are most affected.
During the Pinatubo eruption, strong southwesterly monsoon winds carried ash toward Luzon Island, affecting cities far from the volcano and disrupting air traffic.
Thus, risk levels depend not only on magma composition but also on atmospheric and geographical factors.
Human exposure and settlement patterns also determine the scale of impact.
High population density near volcanoes, such as in Java, Indonesia, increases vulnerability regardless of magma type.
Even less explosive eruptions can be disastrous if they occur near populated areas, as seen in Mount Merapi (Indonesia, 2010), where pyroclastic flows killed over 350 people despite moderate magma composition.
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