Why strato volcanoes explode beige or black lava

How Large Mafic and Felsic Magma Zones Form and Behave

1. Where Mafic and Felsic Materials Come From (Before Melting)

• Mafic material (basaltic) comes from partial melting of the mantle.
  ➔ Temperature: ~1200–1400°C.
  ➔ Silica content: ~45–52% SiO₂.
  ➔ Dense: ~2900–3100 kg/m³.
• Felsic material (granitic/rhyolitic) forms from partial melting of continental crust.
  ➔ Temperature: ~650–800°C.
  ➔ Silica content: ~65–75% SiO₂.
  ➔ Lighter: ~2500–2700 kg/m³.

2. How They Become or Stay Separate

• Physical separation is controlled by:
  ➔ Temperature difference
  ➔ Density difference
  ➔ Viscosity difference
  ➔ Motion inside the magma reservoir

Main ways they stay separate:

• Density stratification: heavier mafic magma sinks, lighter felsic magma floats.
• Crystallization: minerals separate out as the magma cools.
• Temperature gradients: hotter at depth, cooler at the surface preserves layers.

3. How They Mix (or Fail to Mix)

• New mafic magma injected into cooler felsic magma can:
  ➔ Partially melt felsic zones.
  ➔ Form blobs and enclaves without full mixing if viscosities are very different.
  ➔ Cause turbulent mixing only if injection is extremely violent.

4. Large Pockets or Zones

• Size: Kilometer-scale zones possible (hundreds of millions of cubic meters).
• Motion: Extremely slow (centimeters to meters per year).
• Temperature range: 650–1200°C inside the chamber.
• Density-driven layering: Felsic layers stay on top unless disturbed by injections or earthquakes.

Summary in Simple Physical Terms:

Factor	Mafic	Felsic
Temperature (°C)	1200–1400	650–800
Density (kg/m³)	2900–3100	2500–2700
Viscosity	Low (flows easily)	High (sticky)
Movement	Sinks	Floats
Mixing	Poor unless very turbulent	Poor unless very turbulent
Volume scale	~10⁸–10⁹ m³ possible	~10⁸–10⁹ m³ possible