Question 1

Why do some volcanoes erupt explosively and others flow gently?

Accepted Answer

Because of the **viscosity** of the magma and how much **dissolved gas** it contains — and both are determined largely by **silica content**, which in turn depends on the tectonic setting.

**The mechanism.** Magma contains dissolved gases, principally water vapour and carbon dioxide, held in solution by pressure. As magma rises, pressure falls and the gas comes out of solution — exactly as it does when a bottle is opened.

**What happens next depends on whether the gas can escape.**

**Low-viscosity (runny) magma** lets bubbles rise and escape easily. Gas leaves gently, and the eruption is **effusive** — lava flows out. Dangerous to property, rarely to life, since you can walk away from most lava flows.

**High-viscosity (sticky) magma** traps the bubbles. Pressure builds until the magma fragments violently, producing an **explosive** eruption: ash columns, pyroclastic flows and volcanic bombs.

**What determines viscosity.** Principally **silica content**. Silica forms chains that make magma sticky:

**Basaltic magma** — low silica, low viscosity, hotter. Produces effusive eruptions and shield volcanoes with gentle slopes, as in Hawaii and Iceland.

**Andesitic and rhyolitic magma** — higher silica, far more viscous, cooler. Produces explosive eruptions and steep-sided **stratovolcanoes**.

**Why the tectonic setting decides it:**

**Divergent boundaries and hotspots** produce magma derived from the mantle — basaltic and runny.

**Subduction zones** produce magma that has interacted with water-rich sediment and continental crust, becoming enriched in silica and volatiles. **This is why the Pacific Ring of Fire is explosive** — it is a chain of subduction zones.

**Water content** raises explosivity independently, and magma meeting groundwater or seawater produces violent **phreatomagmatic** eruptions.

**The Volcanic Explosivity Index (VEI)** measures eruption size logarithmically, by volume of material ejected and column height.

**What actually kills people:** rarely lava. **Pyroclastic flows** — fast-moving currents of hot gas and ash — are the principal cause, along with **lahars**, mudflows of ash and water that can travel far from the volcano long after an eruption.

Question 2

How do mountains form, and why do they stop growing?

Accepted Answer

Mostly through tectonic collision thickening the crust, and they stop growing because erosion and gravity eventually balance uplift — so a mountain range's height reflects an equilibrium rather than

Question 3

What is the difference between a rock and a mineral?

Accepted Answer

A mineral is a naturally occurring inorganic solid with a definite chemical composition and crystal structure; a rock is an aggregate of one or more minerals. Minerals are the ingredients; rocks are

Question 4

What is plate tectonics?

Accepted Answer

The theory that the Earth's outer shell is divided into rigid plates that move relative to one another over a weaker layer beneath — explaining earthquakes, volcanoes, mountain ranges and the

Question 5

What causes earthquakes, and how is magnitude measured?

Accepted Answer

The sudden release of elastic strain accumulated in rock, and magnitude is measured on a logarithmic scale — which is why the numbers behave in ways people consistently misjudge. The mechanism:

Question 6

How to conduct a simple chemical reaction at home?

Accepted Answer

Conducting simple chemical reactions at home can be fun and educational. Try baking soda and vinegar, lemon juice with baking soda, or milk with vinegar for safe experiments.

Question 7

What actually is fire?

Accepted Answer

Fire is not a substance or an object. It is a process — a self-sustaining chemical reaction — and what you see is the visible byproduct of that reaction. The chemistry. Fire is rapid combustion: fuel

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