Answer:
Water
Explanation:
Water is essential to human life. Hence, human settlements tend to crop up near water sources such as rivers. This is particularly evidence in Africa, which has many quite dry regions.
The reddish-orange colour of weathering of volcanic ash is most likely due to its iron sulfide content which oxidizes to iron oxide so that limonite is yellow and hematite is red and in ash since it is such fine grained material it weathers more rapidly because it has a large surface area.
Pollution, unhealthy materials, plastic.
