Volcanos have constructive effects in favour of man because:
- Lava from plains are very fertile. For example- plains in Java, Malwa region in Deccan plateau and parts of Brazil.
- Lava activity also provides us precious stones.
- Geyser and springs are formed that provide water with health benefits.
- Crater lakes are formed which serve as source of water to perennial rivers. For example-Lake Nyos.
- Sometimes remnants of volcanoes after erosion helps in preserving traces of old civilization.