Understanding Natural Hazards: Earthquakes, Tsunamis, and Volcanic Eruptions
Natural Hazards: Earthquakes, Tsunamis, and Volcanic Eruptions
Earthquakes
Earthquakes are ground vibrations caused by the sudden release of stored energy in the rocks that are under strain. This energy release can cause large rock masses to move, creating fractures called faults.
How an Earthquake Originates
The point where an earthquake originates is called the seismic focus or hypocenter. Seismic vibrations or seismic waves are transmitted in all directions from the focus, similar to the ripples in a pond when a stone is thrown.
How Earthquakes are Measured
Earthquakes are measured by their magnitude using instruments called seismographs. Seismographs draw a graph of the ground motion, called a seismogram. The sensitivity of seismographs allows them to detect even very weak earthquakes that go unnoticed by people.
Earthquake Magnitude
The magnitude of an earthquake is a measure of the amount of energy released. It is measured on the Richter scale, where each grade corresponds to about 32 times the energy released by the previous grade.
Earthquake Frequency
Earthquakes can be classified according to their magnitude:
- Very serious: 8 or greater
- Grave: 7 to 7.9
- Fort: 6 to 6.9
- Mild: 4 to 4.9
- Menor: 3 to 3.9
- Soon: 2 to 2.9
Earthquake Distribution
Most earthquakes occur in areas with high seismicity, which coincide with the boundaries between lithospheric plates. The movement of plates over each other generates earthquakes.
Lithosphere Creation and Destruction
The Earth’s interior is hot, causing materials to move and displace lithospheric plates. New lithosphere is created at oceanic ridges, where plates diverge and holes are filled with materials from the hot interior. Lithosphere is destroyed at subduction zones, where plates converge and one is introduced below the other.
Earthquake Prediction
Currently, there is no reliable system that allows us to know when an earthquake will occur. However, scientists investigate possible earthquake precursors, such as micro-local elevation or alteration of the local magnetic field.
Seismic Risk Assessment
To assess seismic risk, the following factors should be considered:
- Location in relation to plate boundaries
- Local geology
- Seismic history of the area
Earthquake Prevention
Seismic hazard mapping helps identify areas at risk and establish preventive building standards, such as height limits, use of steel structures, and providing elasticity to building structures.
Tsunamis
Tsunamis are a series of huge waves caused by a sudden rise in the volume of a large body of water at the bottom of the sea.
Tsunami Formation
Tsunamis are often caused by earthquakes in subduction zones, where one tectonic plate is forced beneath another. The sudden release of energy from the earthquake causes the seabed to rise, displacing a large volume of ocean water.
Tsunami Propagation
The waves generated by the displacement of water spread in all directions. In the open ocean, they can travel at speeds exceeding 700 km/h. In the high seas, they may be only 1 m high and unnoticed by boats. However, the distance between two peaks can be 200 km, resulting in a large volume of water in each wave.
Tsunami Impacts
As tsunamis approach the shore, friction with the bottom slows them down, causing them to crowd together. The wave narrows and rises, reaching heights of tens of meters.
Tsunami waves can penetrate several miles inland, knocking down buildings and causing widespread destruction. After the first wave, other more destructive waves may follow, lasting for hours.
Tsunami Hazards
Tsunamis are particularly dangerous because:
- They move a huge volume of water, affecting the entire water column from surface to bottom.
- They can travel long distances with little loss of intensity.
- They can cause a withdrawal of the sea before the arrival of large waves.
Volcanic Eruptions
Volcanic eruptions occur when molten rock (magma) rises from the Earth’s interior and erupts onto the surface.
Types of Volcanic Activity
There are two main types of volcanic activity:
- Effusive activity: The lava is very fluid and flows easily out of the crater. Gases escape easily, resulting in few pyroclastic explosions.
- Explosive activity: The lava is very viscous and solidifies, blocking the vent. Gases accumulate and cause strong explosions, projecting pyroclastic material into the air.
Volcanic Hazards
can be due to:
“The emission of toxic gases – Training of pyroclastic flow or pyroclastic,” explosions that accompany the eruption, mud flow or lahar, lava-Wash. How does a volcano?
A volcano is a land surface of the material coming from inside tycoon. The materials ejected by the volcano are: Gases: Water vapor, CO2 and some sulfur compounds, Lava: q is the melt flows from the crater. The lava flows are called lava, pyroclastic, solid materials are projected into the air by the violent escape of gases. From lower to higher dimension are called ash, lapilli bombs and blocks. The melting of rocks in the Earth’s interior causes the magma. The magma always contains a certain amount of gases. The magma rises from the melting zone to the magnetic chamber, q what causes small local earthquake. If you continue coming magma chamber pressure increases, the gases escape and crawl to the other components of magma ascent trip.