Volcanoes? Magma is melted (molten) rock located beneath the Earth’s surface. It is a mixture of melted minerals, crystals, and dissolved gases. 🌋 How is magma related to volcanoes? Magma collects in underground reservoirs called magma chambers. When pressure inside these chambers becomes too high, the magma pushes upward. If it reaches the surface, it causes a volcanic eruption. Once magma comes out of the volcano, it is called lava.
🔥 1. How magma forms
Magma forms when rocks inside the Earth melt due to one or more of these processes:
a) Increase in temperature
Rocks melt when they get hot enough.
This often happens near hot spots or deep in the mantle.
b) Decrease in pressure (decompression melting)
When mantle rock rises toward the surface, the pressure decreases.
Lower pressure allows the rock to melt even without additional heat.
This happens at divergent plate boundaries and mid-ocean ridges.
c) Addition of water (flux melting)
Water lowers the melting point of rock.
This happens where an oceanic plate sinks under another plate (subduction zones).
🧪 2. Types of magma
There are three main types, classified by silica (SiO₂) content:
a) Basaltic magma
Low silica
Very fluid (low viscosity)
Temperature: 1000–1200°C
Produces gentle eruptions (like in Hawaii)
b) Andesitic magma
Medium silica
Thicker (medium viscosity)
Temperature: 800–1000°C
Produces more explosive eruptions
c) Rhyolitic magma
High silica
Very thick (high viscosity)
Temperature: 650–800°C
Causes highly explosive eruptions (like supervolcanoes)
🌋 3. How magma affects volcanic eruptions
a) Silica content controls viscosity
Low silica = runny magma = gentle eruptions
High silica = thick magma = explosive eruptions
b) Gas content affects explosiveness
Thick magma traps gases → big explosions
Runny magma lets gases escape → calm lava flows
c) Temperature
Hotter magma is more fluid and erupts more easily.
