Secondary effect of volcanic activity in environment

Secondary effect of volcanic activity in the Environment

The secondary effects of the volcanic activity include mudflows and the fires. When the large volume of the loose volcanic ash and the other ejections becomes saturated and becomes unstable and moves slowly down the slopes, then, it is called as the mud flows. The catastrophic mud flows occur with little or no warning. They occur when the volcano is hidden by the clouds and the heavy rainfall occurs and after this event, only the few meter of the mud remains. As the mud flows are confined to the valleys, there is another possibility of the hazard when the valley is artificially dammed to produce the hydropower. A large mudflow can fill the reservoir causing the flood that may be devastating.

1. Volcanic products

The volcanic products are classified as:

i. Solid Product

The solid products are also called the tephra which consists the fragments of the pieces of the cooled lava and is also termed as the pyroclast or the pyroclastic material. According to the diameter of the tephra, it is further classified as ;

• Volcanic block

The diameter of the volcanic block is greater than 32mm and the angular shaped.

• Volcanic bomb

The diameter of the volcanic bomb is greater than 32mm and is in the almond shaped with the twisted end. Such twisted ends are formed during the cooling of the magma.

• Cinders

The diameters of the cinders vary from 4mm to 32mm. If the volcanic products are bomb shaped and contain the pore space, then they are called as the vesicle and if they don’t contain vesicle, then they are known as lapilli.

• Volcanic ash

The diameter of the particles lies in between 0.25mm to 4mm.

• Volcanic dust

The diameter of the particle is less than 0.25mm.

ii. Liquid products

The liquid product of the volcanic eruption is only the lava. But according to the distribution of the divalent and the monovalent cation with the percentage of the silica (SiO2), the lava is classified into :

• Mafic Lava

The lava is said to be mafic lava, if the lava contains a higher percentage of the magnesium, iron, calcium and lesser percentage of the silica (<50%). This lava has low viscosity and the temperature is in around 1000-2000 ⁰C. It has low vapour pressure and tends to quite the eruption.

• Intermediate Lava

The lava is said to be intermediate lava, if the silica percentage is in between 55%- 66% and may contain divalent cation like Mg⁺⁺ ,Ca⁺⁺ and monovalent cations like Na⁺, K⁺ in 40%- 45%.

• Felsic Lava

The lava is said to be felsic lava, if the silica percentage is more than 60% and the maximum cations of Na and K are present. The temperature of this lava is 800- 1000 ⁰C and contain high volatile material. These have high viscosity and are violent in eruption.

iii. Volcanic gases

The total amount of the volcanic gases effuses during volcano eruption is only about 1% by weight. About 90% of water vapour is present in the gases form. Besides the water vapour, the other toxic gases are the fumes of H₂SO₄ , Phosphoric acid, boric acid and other acid vapours. The acid gases cause acid rain around the volcanic region for about 5 years.

Features associated with the Volcanism and the Volcanic Topography

Normally in common sense, the volcano is thought to have a conical mountain with the circular base and the pointed top.,Depending upon the nature of product and how they accumulate volcano builds a variety of land is formed. These volcanic landforms include volcanic plains and the plateaus, volcanic cone, volcanic shields, craters and the cinders.

1. Volcanic plains and volcanic plateaus

These volcanic plains and plateaus are the flat sheets of the extrusive igneous rocks formed from the fluid mafic lava. The difference between the volcanic plains and the 3 plateaus is the height of the surface compared to the surrounding countryside. The plane is the low standing areas of the even thickness of several kilometres.

2. Volcanic cones

The volcanic landforms in forms of the cone are also popular and the several varieties are recognised depending upon the material composing them.

• Tephra cones or the cinder cones

These consist of the fine-grained uniform sized tephra that is ejected from the circular volcanic vent and is piled up surrounding the vent.

• Lava Cones

They are the built up of the lavas due to the piling up of the lava during an eruption.

• Composite Cones

These types of the scenes are composed up of the sloping layers of tephra and the reinforcing layers of the lava.

• Craters

These are the depression located at the summit of the volcanic cone and is usually funnel-shaped hollow from where the pyroclastic materials, gases, as well as the liquid lavas, are ejected. The craters usually have depression less than 1.5 km.

• Volcanic shields

These are broad, gently sloping (80 or the less amount) of the volcanic rock and are the quite eruptions of the highly fluid mafic lava from the circular vent.

• Calderas

These are the circular features having a diameter greater than 1.5 km and are formed by collapsing the upper part of the conical summit. The circular depressions commonly have steep inner walls and the flat floor.

Effect of Volcanic Activity on the Environment

The eruption of the volcanoes on each year brought various types of the damage by the lava flows as the shower of the tephra and the noxious gases. The lava flow from the eruption can cover the roads and the villages and cause firing on the forests and homes. The sulphur dioxide from the eruption reaches to the atmosphere, gets converted to the tiny droplets and remains for a long time. The other gases like HCl, Boric acid and the arsenic acid may fell back during the rainy season in the form of acid causing acid rain which may damage biotic and the abiotic components of the environment.

In spite of, the negative impacts the volcanic eruption also provide some benefits in the form of majestic mountains some lakes and other land forms to live on and fertile soils for the agriculture. The tephras spread out on the surface provide instant soil and contain many plant nutrients.

References:

Keller, E.A. Environmental Geology. Columbus, Ohio: Charles E. Miller Publishing Company, Bell and Howell Company, 1985.

Mahapatra, G.B. Textbook of Physical Geology. Shahadra,Delhi-110032: CBS Publishers and Distributers Pvt.Ltd., 1992.