Volcano signs
Volcanic bombs
These pieces have oval or spherical shape. Their
length varies between a couple of centimeters to
several meters originating from acidic to intermediate
explosive volcanoes. Volcanic bombs special shape is
due to rotation of molten materials in the air coming
out from volcanoes’ craters. If magma is very dense,
the effects of rotation will not be observed in it,
but after cooling process several cracks appear on
them. These volcanic pieces are very similar to a
loaf of bread.
Scoria
Sometimes, basaltic volcanoes having less viscous
magma throw pieces of molten materials into the air.
In this case, these materials solidify because of cold
weather. Their shape is irregular having red color
with less porosity. They are called scoria.
Lava
Hot, boiling material consists of different silicates
having less water vapor and gas in comparison to
magma. Lavas’colors are red, yellow and white. These
colors are due to high heat of lava while coming out
from crater. Lavas can be acidic, intermediate or
basic. Basic lavas are less viscous in comparison to
acidic type. They flow faster and cover larger areas.
In lava scattering process, concentration, gases’
volumes, region’s dip and shape of flowing lava and
pressure has significant role. Concentration of lava
decreases, but temperature increases in closer areas
to the crater. Within gradual cooling of lava,
minerals are crystallized. Due to insufficient time
for crystal growth, fine grain rocks are formed.
Volcanic glasses, such as obsidian are the result of
fast cooling process of lava. It has a lot of pores
like certain volcanic rocks (eg.pumice). These pores
produce when gases emitting from lava within its
cooling. The oldest lavas of Iran belong to
Precambrian, which are completely metamorphosed.
Volcanic ash
These particles are finer than 2mm, light, smooth and
very similar to powder. Volcanic ash is made of
feldspars, leucite, augite, magnetite, etc. It
originates from fine grains of lava, crushing of
chimney’s rocks and even from collision of solid
particles in volcanic ash within lava eruption from
crater. Sometimes, fine grain ash can be suspended in
air, such as Krakatoa (1883) and Bezymianny (1956).
The ash of these volcanoes rotates around the globe
several times, before precipitation. Although, ash
deposition can be harmful, but it can fertilize
lands’soils and assist human being.
Volcanic sands are another form of particles coming
out of crater. They are produced similar to ash but
their size is bigger. The result of ash precipitation
in sedimentary basins is the production of pyroclastic
rocks called tuff.
Volcanic gases
Gases are observed in all stages of volcanic activity,
and they are the signs of active and semi-active
volcanoes. The solubility of gases depends on magma’s
pressure and temperature. Based on soluble gases in
magma, Yager has classifed different types of magma as
follows;
Yager classification
1.Hypomagma: It is a magma type, which is under very
high pressure and rich of dissolved gases.
2.Pyromagma: It is a gas bearing magma type, which
gases tend to emit but they have not formed a separate
phase, yet.
3.Epimagma: It is a magma type having lost its gases,
but liquid and gas parts have produced two separate
phases.
Lahar
A mudflow composed chiefly of volcaniclastic materials
and ash on the flank of a volcano is called Lahar. It
can carry big pieces of rocks and also produce plenty
of damage on the way of its flow.
Lapilli
Particles having diameter of 0.2 to 3cm made of
volcano chimney rocks and lost their water are called
lapilli. Certain types of lapilli have made of acidic
lavas and have porous texture called perlite. It is
used in making buildings.
Ponce or pumice
Glassy, solid, light, acidic and porous materials
emitting from volcano crater by pressure is called
ponce or pumice. Diameter of pumice may reach up to
10cm. Pumices, due to high porosity and low viscosity
remain on the surface of water. Although pumice sizes
are different from ash, but they are precipitated
after ash in a liquid environment. Ponces have
different types, such as pumice stone, which is a dark
stone originating from intermediate to basic basalts.
Pumice density is less than one.
Geysers
Geysers are type of hot springs that intermittently
erupts jets of hot water and steam, the result of
ground water coming into contact with rock or steam
hot enough to create steam under conditions preventing
free circulation. Their activity period varies
between a couple of minutes to several days. Then,
they will become inactive. Geysers’ height and
temperature is very different. Their temperature
varies between 8C to 100C, and their height can be up
to 50m. Geysers do not have permanent activity. They
appear in the regions of newly occurred volcanic
activities.
How does a geyser act?
A geyser is the result is of underground water under
the combined conditions of high temperatures and
increased pressure beneath the surface of the Earth.
Since temperature rises under the Earth’s surface, and
pressure increases with depth, water that seeps down
in cracks and fissures until it reaches very hot rocks
in the Earth’s interior becomes heated to a high
temperature. Because of the greater pressure, it
shoots out of the surface in the form of steam and hot
water. The result is a geyser.
They include certain materials, such as silica,
therefore, some mineral sediments are observed around
them.
Hot water springs
Hot water springs are natural and their water
temperature is a couple degrees higher than
environment temperature. Factors increasing the water
temperature of these springs are different. For
instance, geothermal energy, nuclear, chemical and
earthquake displacement is some of these factors. Hot
water springs may occur in two forms;
1.In volcanic regions, water passes through faults and
fractures. During this process, water gradually warms
up. After reaching the surface, it makes hot water
springs. In accordance with depth and emission speed
of water, it has higher temperature.
2.Cooling stage of magma occurring inside the ground
produces water steam. It moves upwards by water vapor
and gases pressure.
Most of hot water springs of Iran are in relation to
volcanism, like hot water springs of Ab-e-Ask, Sareyn,
Bilehrood, Mahalat, etc.
Ab-e-Ask hot water springs
It is 96km away from eastern Tehran and it is in the
south flank of mount Damavand, close to the Haraz
river. The location of Ab-e-Ask hot water springs on
Jurassic limestones bearing acidic water and sulfur.
Different opinions are available respecting the origin
of these springs. Some of them are as follows;
-Warming of intrusive waters available behind Lar dam.
-Volcanic activity could produce these springs,
therefore, its origin is hydrothermal.
Sareyn mineral springs
These springs located 2km away from western Ardebil.
It is the result of Sabalan volcanic activity. This
village has several springs with different names.
Among these springs, Gavmish goli? is the most
important. The water of these sulfuric springs is a
little dark. It temperature is about 42 to 47C, and
its taste is sour.
Mahalat hot spring
It is located in southwestern Tehran and 30km away
from western Delijan. It is on the heights of this
region. Around these springs huge travertin mines can
be observed, which is the result of sedimentation in
this region. The water temperature of this spring is
due to volcanic activity. Surface waters inject into
fractures and dissolve calcareous materials. Two
formations of the Mahalat Mountains belong to
Jurassic.
