🌋 Lava Flow Rheology

About this simulation

Lava is a fluid, and like any fluid it has a viscosity — its resistance to flowing. Two compositional factors dominate that viscosity: temperature and silica (SiO₂) content. Hot, low-silica basaltic lava flows almost like thick syrup, spreading in broad, fast-moving sheets. Cooler, silica-rich lava behaves more like toothpaste, creeping slowly inside self-built channels lined with solidified levees.

How it works

• Silica content — SiO₂ molecules link into long polymer chains in the melt; more silica means more chain cross-linking and dramatically higher viscosity.
• Temperature — heat gives molecules more thermal energy to break those chain bonds, lowering viscosity roughly exponentially as temperature rises.
• Flow regime — low viscosity favours wide, thin, fast sheet flows (like Hawaiian pāhoehoe); high viscosity favours narrow, thick, slow channelized flows with built-up levees (like andesitic aa flows), and very high viscosity can stall into a dome.
• The glowing lava cools and darkens as it travels from the vent, forming a crust while the interior stays molten.

Controls

• Temperature — eruption temperature of the melt (900–1200°C).
• Silica content — weight % SiO₂, from basaltic (45%) to dacitic/rhyolitic (75%).
• Slope angle — steepness of the volcanic flank the lava descends.
• Effusion rate — how much lava is being erupted, controlling flow volume.
• ↺ Reset flow — clears the current flow. Drag to rotate, scroll to zoom.

Did you know?

Basaltic lava viscosity can be as low as 10–100 Pa·s (about like ketchup), while silica-rich rhyolitic magma can exceed 10⁹ Pa·s — roughly a billion times stiffer — which is why rhyolite erupts explosively instead of flowing.