Lesson Summary: Geohazards
Hello, future TCAS candidates! The topic of "Geohazards" in Applied Science is a frequent exam focus and a great way to boost your score. It’s mostly about natural phenomena we often hear about in the news. If you feel like there’s a lot of content, don't worry! I’ve summarized the key points you need for the exam using language that’s easy to grasp.
In this chapter, we’ll learn how our Earth "moves" and "erupts," as well as how to stay safe.
1. Earthquakes
Earthquakes are caused by the vibration of the Earth's surface due to the sudden release of energy accumulated within the crust.
Main Cause:
Most are caused by the movement of "Tectonic Plates"—whether they collide, pull apart, or slide past one another. This movement creates faults where energy builds up until the rock can no longer withstand the stress, causing a sudden release.
Key Distinctions:
- Hypocenter (Focus): The point underground where the earthquake actually begins.
- Epicenter: The point on the Earth's surface directly above the hypocenter (this is the location usually reported in the news, like a specific district or province).
Magnitude vs. Intensity:
Students often confuse these two, so use this principle to remember:
- Magnitude: The amount of energy released. There is only one value per event, measured by a Seismograph. Common units include the Richter scale or the Moment Magnitude scale.
- Intensity: The felt experience of people and the actual damage caused. There can be multiple values depending on the distance from the epicenter, measured by the Mercalli scale.
💡 A simple analogy: Magnitude is like the wattage of a lightbulb (it’s constant), while intensity is like the brightness you see (the further away you are, the dimmer the light, and the lower the intensity).
Did you know? Thailand has active faults mainly in the North, West, and South, such as the Mae Chan fault and the Si Sawat fault.
Common Pitfall: Students often think the magnitude of an earthquake changes based on location. In reality, magnitude has only one value, while the intensity changes according to distance.
Key Summary: Be sure to clearly distinguish between "Hypocenter" vs. "Epicenter," and "Magnitude" vs. "Intensity!"
2. Tsunamis
A tsunami is not a wind-driven wave; it is a giant wave caused by the displacement of a massive volume of water.
How it forms:
Most are caused by undersea earthquakes involving vertical movement, which suddenly pushes or drops a massive volume of water, creating waves that spread in all directions.
Characteristics of a Tsunami:
- In deep sea: The wave height is very low (almost invisible), but it travels incredibly fast (as fast as a jet plane!).
- Near the coast: As the water gets shallower, the speed decreases, but the massive energy causes the wave height to increase rapidly.
Warning Sign: If the sea level recedes abnormally fast, exposing the beach, run to higher ground immediately! That is a sign that a giant wave is coming.
Key Summary: Tsunamis are caused by water displacement (usually from vertical seafloor movement). The shallower the water, the taller the wave.
3. Volcanic Eruptions
A volcano is an opening in the Earth's crust that allows Magma and underground gases to escape.
Vocabulary to know:
- Magma: Molten rock located beneath the Earth's surface.
- Lava: Molten rock that has erupted and is on the Earth's surface.
Impacts of Volcanoes:
- Volcanic Ash: Fine dust that can travel long distances, block sunlight (temporarily cooling the Earth), and damage aircraft engines and respiratory systems.
- Toxic Gases: Such as sulfur dioxide.
- Pyroclastic Flow: A mixture of hot gas and rock fragments that flows down slopes at high speeds (the most dangerous part!).
Did you know? The area with the highest concentration of volcanoes in the world is called the "Ring of Fire," located along the edges of the Pacific Ocean.
Key Summary: Volcanic eruptions are caused by heat, pressure, and tectonic plate movement. The impact isn't just lava—it includes ash and hazardous gases.
4. Landslides
A landslide is the movement of soil or rock masses down a slope due to gravity.
Contributing Factors:
- Heavy, continuous rain: Water infiltrates between soil particles, reducing friction and increasing the weight of the soil.
- Slope steepness: The steeper the slope, the higher the risk.
- Deforestation: A lack of tree roots to hold the soil in place.
Warning Signs: Stream water becoming muddy or matching the color of the soil on the mountain, hearing rumbling sounds from the forest, or a rapid rise in water levels in a creek.
Key Summary: Heavy rain + bare mountains = high landslide risk.
🌟 Exam Techniques (Memory Aids)
1. Tsunami: Think of "depth" -> Deep = fast but low, Shallow = slow but high.
2. Earthquake: "Hypocenter" (Focus) is deep down, "Epicenter" is on the surface.
3. Lava vs. Magma: Magma (M = Mother, stays inside), Lava (L = Leave, it has left and come out).
If you find this difficult at first, don't worry! Keep reviewing and practicing problems, and you'll find that Geohazards is one of the best chapters to score well on in your A-Level Applied Science! You've got this!