CHAPTER 3 VULCANISM AND EARTHQUAKES
Landforms Associated with Vulcanic Activities
Vulcanic activities have a profound influence on the earth’s landforms. Solid liquid or
gaseous materials may find their way to the surface from their deep seated reservoir
beneath. Molten magma is mobile rock that forces its way into the plains of weakness of the
crust to escape quietly or explosively to the surface. Magma while thrusting its way up to
the surface may cool and solidify within the crust as plutonic rocks resulting in intrusive land
forms. Magma that reach the surface and solidify, form extrusive landforms. Rocks formed
by either plutonic or volcanic activity are called igneous rock.
Landforms of Igneous intrusions
The common intrusive landforms include sills and dykes. When an intrusion of molten
magma is made horizontally along the bedding planes of sedimentary rocks, the resultant
intrusion is called a sill. When injected vertically, as narrow walls of igneous rocks within the
sedimentary layers are termed as dykes.
Igneous intrusions on a larger scale are the various types of
‘_liths’:laccoliths, lopoliths, phacoliths and batholiths. A laccolith is a large blister or igneous
mound with a dome shaped upper surface and a level base fed by a pipe-like coduit from
below. It arches up the overlying strata of sedimentary rocks., eg. the laccoliths of the Henry
Mountains, in Utah U.S.A.
A lopolith is another variety of igneous intrusion with a saucer shape. A
shallow basin is formed in the midst of the country rocks. A phacolith is a lens shaped mass
of igneous rocks occupying the crest of an anticline or the bottom of a syncline and being
fed by a conduit from beneath. A batholith is a huge mass of igneous rocks, usually granite,
which after removal of the overlying rocks form a massive and resistant upland region such
as the Wicklow Mountains of Ireland.
THE ORGIN OF THE VOLCANOES
Then magma is heavily charged with gases such as carbondioxide, sulphurated hydrogenand
small prpotions of niotrogen, chlorine and other volatile substances. The gases and vapour
increases the mobility and explosiveness of the lavas which are emitted through the vent of
a volcano during a volcanic eruption. There are two main types of lavas.
1.Basic lavas:
These are the hottest lavas, about 1000 degree Celsius and are highly fluid. They are dark
colored like basalt, rich in iron and Magnesium, but poor in Silica.
Landforms Associated with Vulcanic Activities
Vulcanic activities have a profound influence on the earth’s landforms. Solid liquid or
gaseous materials may find their way to the surface from their deep seated reservoir
beneath. Molten magma is mobile rock that forces its way into the plains of weakness of the
crust to escape quietly or explosively to the surface. Magma while thrusting its way up to
the surface may cool and solidify within the crust as plutonic rocks resulting in intrusive land
forms. Magma that reach the surface and solidify, form extrusive landforms. Rocks formed
by either plutonic or volcanic activity are called igneous rock.
Landforms of Igneous intrusions
The common intrusive landforms include sills and dykes. When an intrusion of molten
magma is made horizontally along the bedding planes of sedimentary rocks, the resultant
intrusion is called a sill. When injected vertically, as narrow walls of igneous rocks within the
sedimentary layers are termed as dykes.
Igneous intrusions on a larger scale are the various types of
‘_liths’:laccoliths, lopoliths, phacoliths and batholiths. A laccolith is a large blister or igneous
mound with a dome shaped upper surface and a level base fed by a pipe-like coduit from
below. It arches up the overlying strata of sedimentary rocks., eg. the laccoliths of the Henry
Mountains, in Utah U.S.A.
A lopolith is another variety of igneous intrusion with a saucer shape. A
shallow basin is formed in the midst of the country rocks. A phacolith is a lens shaped mass
of igneous rocks occupying the crest of an anticline or the bottom of a syncline and being
fed by a conduit from beneath. A batholith is a huge mass of igneous rocks, usually granite,
which after removal of the overlying rocks form a massive and resistant upland region such
as the Wicklow Mountains of Ireland.
THE ORGIN OF THE VOLCANOES
Then magma is heavily charged with gases such as carbondioxide, sulphurated hydrogenand
small prpotions of niotrogen, chlorine and other volatile substances. The gases and vapour
increases the mobility and explosiveness of the lavas which are emitted through the vent of
a volcano during a volcanic eruption. There are two main types of lavas.
1.Basic lavas:
These are the hottest lavas, about 1000 degree Celsius and are highly fluid. They are dark
colored like basalt, rich in iron and Magnesium, but poor in Silica.
