Tsunami Formation and Volcanic Eruption Dynamics

How a Tsunami Forms

In the subduction zone, the oceanic lithosphere enters the Earth's interior. The upper end of the plate is locked and dragged down, building up tension.

The sudden release of this tension generates the seismic field. The seabed rises, displacing a huge volume of water upward.

Waves generated by this movement spread in all directions.

As they approach the coast, friction with the bottom slows the wave down. The wave narrows and rises, potentially reaching tens of meters high.

The wave can penetrate several miles inland. After the first wave, others, potentially more destructive, may arrive, lasting several hours.

Tsunami Alert System

The seismograph detects earthquakes and sends the information to the host system.

If the magnitude is above 6.5, the central computer sends a notice to countries at risk.

Floating buoys detect the tsunami, gather data, and refer it to the host system.

The central computer processes the information, predicts the propagation speed, and transmits the alert signal to the affected areas.

Tsunami Characteristics

A tsunami involves moving a huge volume of water: water moves from the surface to the bottom. The wavelength is very large, as is its volume.

It propagates with little loss of intensity, meaning its effects reach remote areas.

Usually, there is a withdrawal of the sea minutes before the arrival of the large waves.

What to Do in Case of a Tsunami

• If you are in a boat offshore, remain there; the destructive tsunami is just off the coast.
• If alerted, move to higher ground, ideally 30 meters above sea level.

How a Volcano Functions

A volcano is a place on the Earth's surface where magmatic material exits from the interior. The ejecta can be:

• Gases: Water vapor, CO2, and some sulfur compounds.
• Lava: Molten material flowing from the crater. Lava flows are called castings.
• Pyroclastic: Solid materials thrown into the air by the violent escape of gases. From smallest to largest dimension, these are called: ash, lapilli, bombs, and blocks.

The melting of rocks in the Earth's interior causes magma, which rises from the melting zone to the magma chamber, causing small local earthquakes.

What Makes an Eruption Dangerous

Types of Volcanic Activity:

• Effusive: Low-viscosity lava flows smoothly from the crater. Gases escape easily, resulting in few explosions and scarce pyroclastics.
• Explosive: Very viscous lava blocks the vent. Gases accumulate, causing strong explosions that project a large, more dangerous amount of pyroclastics into the air.

Volcanic Hazards Include:

• Emission of toxic gases
• Formation of pyroclastic flows
• Explosions
• Mud flow or lahar
• Lava flows

Precursors of an Eruption Are:

• Small local earthquakes, generated by magma movement in the chamber and the opening of fractures.
• Changes in the slope of the land.
• Temperature rise of water wells.
• Increase in greenhouse gas emissions.