How can pyroclastic clouds and lahars affect the environment?

The pyroclastic clouds are formed during the time of the volcanic eruption and this cloud is comprised of a large number of harmful gases such as SO₂, CO, H₂S, CO₂ and H₂O (water vapor). These gases are then mixed with the atmosphere causing air pollution. Excessive emission of gases leads to the formation of large clouds that do not allow the sunlight to penetrate and reach the surface.

The lahars are also formed during the time of volcanic eruptions, that flows down along the slope of the mountains. As it flows down it melts the snow and also burns up the usable land areas and deposits the volcanic sediments, thereby degrading the soil fertility.