The Viscosity Vent
Hawaiian lava runs downhill like syrup; Cascade magma of the same temperature blows the top off the mountain.
Phase 0 · The phenomenon
Syrup or shrapnel
Left: a broad, gently sloping shield volcano with a long orange lava flow running down its flank. Right: a steep cone-shaped stratovolcano with a tall grey eruption column of ash billowing from its summit.
On Kīlauea, rivers of glowing basalt lava run for kilometres down gentle slopes, so runny that geologists can dip a hammer into them. The volcano grows into a broad, low shield.
In the Cascades, Mount St. Helens did something else entirely in 1980: its magma never flowed at all. It burst apart into ash and pumice that rose 24 kilometres into the sky.
Even if you heated both magmas to the same temperature, they would behave nothing alike. In this lab you will measure why — and trace both magmas back to where they melted.
Why does one magma flow like syrup while another, at the same temperature, explodes — and where does each kind of magma come from?
What this lab works toward
HS-ESS2-1Model how Earth's internal and surface processes, working at different sizes and speeds, build continents and ocean-floor features.HS-ESS2-3Model, from evidence about Earth's interior, how heat-driven convection cycles matter.
Plain-English summaries. The course maps these performance expectations to this lab; the official wording is published at nextgenscience.org.
The stations
- Silica DialHow much does silica content change a magma's viscosity at one temperature?
- Flow SpeedHow do viscosity, temperature and slope set the speed of a lava flow?
- Gas EscapeWhy does rising rhyolite magma explode while basalt fountains?
- Melt ColumnWhy does hot mantle melt beneath a hotspot or a ridge but not beneath ordinary thick plates?
Each station runs the same loop: predict before you see any data, investigate the model and record runs, reveal what the measurements show, then explain the gap between your prediction and the result. A claim-evidence-reasoning checkpoint and an exit ticket close the lab.
- Viscosity comes from a studio fit to published ranges for crystal-free, dry melts. Crystals make real magma stiffer, and dissolved water makes it much runnier.
- Lava speed uses Jeffreys' formula for a wide, uniform 1 m-thick flow on a constant slope. Cooling crusts and channels change real flows.
- Gas escape tracks only water. Real magmas also carry carbon dioxide and sulfur gases, and bubble growth takes time, which the model ignores.
- The melting station uses one solidus for dry mantle peridotite and a fixed adiabat. Water lowers the solidus — the reason subduction zones melt — and is not modelled here.