🌋 Week 3: Volcanic Eruption Styles & Magma Properties 🔥

🌋 The Challenge: Two Volcanoes, Same Process — Completely Different Results

Watch the two eruption clips your teacher shows. One is Mount St. Helens (1980) — it blasted sideways with an explosion visible for hundreds of miles. The other is Kilauea in Hawaii — tourists stand within a few hundred meters watching lava ooze into the ocean.

Both are volcanoes. Both involve magma reaching the surface. So why are they so different? Your job today is to figure that out.

✋ Stop & Think — Before You Open the Form

Based on what you know about plate boundaries from Weeks 1 and 2, pick a prediction for each volcano:

• Mt. St. Helens (Washington State, Pacific coast): sits on a _____________________ boundary
• Kilauea (Hawaii, middle of Pacific Ocean): sits over a _____________________

Write your prediction on your worksheet, then open the form below to record your observations.

📖 The Scenario

A scientist collected data about two volcanoes. Your job: use the data to predict what each eruption will look like and what landform each volcano will build.

🔢 Step 1: Identify the Silica Percentage and What It Means

Look at the silica column. Volcano A has 75% silica — Volcano B has 50%. Silica (SiO₂) forms long, cross-linked mineral chains in magma. The more chains, the thicker the magma.

Rule: Higher silica % → more SiO₂ chains link together → magma is thicker → higher viscosity. Volcano A = very viscous. Volcano B = very fluid.

🔢 Step 2: Connect Viscosity to Gas Trapping

All magma contains dissolved gases (mostly water vapor and CO₂). As magma rises, pressure drops and gas tries to escape — like bubbles in a soda bottle when you open it.

In thick (high-viscosity) magma, the gas cannot escape through the sticky magma. Pressure builds and builds until — BOOM. In thin (low-viscosity) magma, gas bubbles rise and escape easily, like in flat soda.

🔢 Step 3: Predict the Eruption Style

Using the silica-viscosity-gas connection:

• Volcano A (75% silica, very high viscosity): Gas is trapped → pressure explodes the magma into ash, rock fragments, and pyroclastic flows → Plinian / explosive eruption
• Volcano B (50% silica, very low viscosity): Gas escapes easily → lava oozes out quietly → Hawaiian / effusive eruption

🔢 Step 4: Predict the Landform Built

Eruption style determines the shape of the mountain: Volcano A builds a tall, steep-sided stratovolcano (layers of ash and lava, like Mt. St. Helens). Volcano B builds a wide, gently sloping shield volcano (runny lava spreads far, like Kilauea / Mauna Loa).

⚠️ Common Mistake: "Hotter = More Explosive"

Many students think hotter lava erupts more explosively. This is backwards.

Hotter magma is more fluid (lower viscosity) → gas escapes easily → less explosive. Cooler, silica-rich magma is thicker → gas is trapped → more explosive. Temperature matters, but silica content is the key control on viscosity.

✏️ Now You Try

A geologist finds a new volcano with 62% silica content and 900°C magma. Using the four-step process:

1. What is the approximate viscosity? (low / moderate / high)
2. Can gas escape easily or does it get trapped?
3. What eruption type would you predict? (effusive, Strombolian, or explosive Plinian)
4. What landform would likely form?

Write your answers on your worksheet before moving to Station 1.

💻 Simulation: Magma Viscosity

🔥 What You Are Investigating

You practiced the four-step method in the worked example. Now you will apply it to three real magma types using actual volcanic data. Use the reference table below to answer the form questions.

Key mechanism to remember: High silica → SiO₂ chains link together → magma too thick for gas to escape → pressure builds → explosion.

📊 Reference Table: Magma Types

💬 Sentence Starters (Use These in Your Form Responses)

• "I predict Volcano X will have a [type] eruption because its silica content is ___%, which means..."
• "The evidence that supports my prediction is..."
• "Higher silica content leads to higher viscosity because..."

💻 What You Are Analyzing

Volcanoes don't just produce lava. They generate a range of hazards — some slow and avoidable, others faster than a car. In this station you will compare the five main volcanic hazards and rank them by danger using evidence from the table below.

Key concept: Pyroclastic flows — clouds of hot gas, ash, and rock — travel at 100–700 km/h at temperatures up to 800°C. They killed 30,000 people in Martinique in 1902 in under two minutes. No one can outrun them.

📊 Reference Table: Volcanic Hazard Comparison

💬 Sentence Starters (Use These in Your Form Responses)

• "Pyroclastic flows are more dangerous than lava flows because..."
• "Warning time matters for survival because..."
• "The most important factor in determining hazard level is ___ because..."

🛠️ Your Engineering Challenge

You are a volcanologist hired by the government of a country with a large active volcano near a city of 50,000 people. Your job: design a monitoring network that can detect an eruption at least 72 hours in advance so people can evacuate safely.

Constraints: $2 million budget • Must cover a 10 km radius • Must use at least 3 different sensor types • Must provide 72+ hours of warning.

📊 Reference Table: Available Monitoring Sensors

💬 Sentence Starters (Use These in Your Design Justification)

• "I chose the [sensor] because it detects ___, which tells us that..."
• "Using multiple sensors is important because one sensor alone cannot..."
• "My system would give 72 hours of warning because..."