Lava can be defined as molten rock erupting from volcanic vents. A large amount of lava stays within the earth known as magma in geological terms. During a volcanic eruption, magma is forced out of the mouth of the volcanic vent in the form of molten lava.
There are various types of volcanoes like: – wide shield volcanoes, mounded lava domes and steep volcanoes. The type of a volcano depends on the type of lava it is made up of.
Types of lava: –
- Pahoehoe lava: – It is a continuous and smooth lava crust. This type of lava forms when the effusion rate is low as it decreases the velocity of lava flow. Pahoehoe lava can be formed by only low viscosity lava. This type of lava is also known as ropy lava. The best example for this type of lava flows are from the Big Island of Hawaii.
- Aa lava: – It is a very common form of lava flow. Aa lava is a rough and rubble crust of a lava flow. The word ‘aa’ has been derived from the Hawaiian language. This type of lava flow is not safe for walking at all because the uppermost layer is made up of loose clinkery blocks that are not stable. You may easily loose balance while walking on them as the rock keeps moving. Southern tip of La Palma is a good example of the internal structure of aa lava.
- Blocky lava: – Block lava flow forms when the silica content is higher in lava. Blocky and aa lava flow resemble each other. Lava blocks have irregular surfaces but their edges and sides are smoother compared to separate pieces of aa lava. Nea Kameni Island in the caldera of Santorini, Greece is an excellent example of Blocky lava flow.
- Pillow lava: – Pillow lava is the most common type of lava. It is always associated with water. This type of lava flow forms when lava flows out of the earth’s crust underwater. Generally pillow lava erupt at mid ocean ridges but they can also form in shallow water bodies like lakes or glacial ice. Each and every pillow looks like a bag. This lava flow has a glassy surface because it cools down quickly in contact with water.