Volcanos i need to know more

Two volcanoes, built from the same hot rock beneath them. Kilauea oozes — runny lava flowing like a slow, smooth melody. Mount St. Helens blows its top like a crash cymbal.

Same rock, same heat. So why the difference? Every volcano follows the same route. Deep underground, heat melts rock into magma.

Magma is lighter than the rock around it, so it rises and pools in a magma chamber, where dissolved gas builds pressure. Then the drop: it erupts through a vent. What happens next comes down to two things — gas and stickiness. Runny lava builds a broad shield volcano; sticky lava builds a steep one, like this cross-section.

Start deep underground. Earth's interior is hot enough to melt rock, and in the mantle that is exactly what happens. At a subduction zone, water is dragged down with the sinking plate, and water lowers the melting point, so more rock melts and magma forms. Magma is less dense than the solid rock around it, so it rises, the way a loud low note pushes up through a quiet mix.

A few kilometres down it pools in a magma chamber, where pressure holds water vapour, carbon dioxide and sulphur dioxide dissolved inside it. As the magma climbs, pressure drops. Gas comes out of solution, bubbles expand, and water turning to steam swells more than a thousand times over. Gas and silica decide the style.

Basalt is about fifty per cent silica and nearly twelve hundred degrees: runny, bubbles escape easily, lava fountains and flows — effusive, a smooth melody. Magma near seventy per cent silica is sticky, its bubbles cannot escape, and pressure builds until the rock above fails — explosive, a held chord slamming into a crash. The products come out as lava flows, ash fall, pyroclastic flows, lahars and gas. And eruption after eruption stacks them into the landform: broad shield volcanoes from runny flows, steep layered stratovolcanoes from ash plus lava.

The stickier the magma, the more gas it traps — and the bigger the bang. That single sentence is the crux this whole video hangs on. Runny magma oozes out quietly; sticky magma erupts. Take Kilauea, in Hawaii.

Its magma is basalt: about fifty percent silica, and around twelve hundred degrees Celsius. Enormous heat — but silica is what makes magma sticky, and half isn't much, so viscosity stays low. Gas bubbles rise and simply pop. So no blast: just lava fountains and slow flows, creeping along at walking pace.

People step aside rather than run. That's the smooth legato line from our opening question — the same notes, played softly. Surtsey, 1963. Beneath the sea off Iceland, runny basalt magma rises — the kind that should simply ooze.

But seawater meets it, flashes instantly to steam, and that steam shatters the magma into fine ash and glass. The blast is violent, and it built a new island. So here it is the water, not the silica, that decides — the stickiness rule has an exception. Let's run the whole map one more time.

Interior heat melts rock, and magma rises. Gas stays dissolved while the pressure is high; as the pressure drops, bubbles grow. Stickiness then decides: gentle ooze, or violent blast. That builds shield volcanoes or stratovolcanoes.

So it's the gas and the stickiness — not the size of the volcano. The same music, played with different dynamics.