Lava Flows
Lava is molten rock expelled by a volcano during a non-explosive eruption. The temperature and viscosity of lavas determine how the lava will behave. Silica-poor basaltic magmas with high temperature and low viscosity are very fluid and develop a range of fluidal shapes, while cooler viscous rhyolitic flows often break up into blocks which are then reincorporated into the lava flow again, a process called autobrecciation.
Massive Basalt
Low viscosity degassed basaltic flow
Size: 12 cm
Aa-Lava
Low viscosity lava flow with rough and fragmented surfaces
Size: 12 cm
Aa-Lava - is more viscous than Pahoehoe lava
Hawaii, USA
Size: 10 cm
Pahoehoe Lava
Low-viscosity lava flow with smooth and ropy surfaces
Size: 13 cm
Pahoehoe Lava – is less viscous than Aa lava
Zhejiang, China
Size: 20 cm
Rhyolite
Highly viscous degassed lava with flow banding
Size: 15 cm
Volcanic Breccia - formed by autobrecciation
Sai Kung, Hong Kong
Size: 16 cm
Volcanic Breccia - Usually found in thick nearly solidified lava flows
Sarawak, Malaysia
Size: 12 cm