BHIVARABAI SAWANT COLLEGE OF ENGINEERING
AND RESEARCH, NARHE, PUNE.
(JSPM GROUP OF INSTITUTE)
DEPARTMENT OF
CIVIL ENGINEERING
A REPORT ON “GEOLOGICAL SITE VISIT TO MMCC,
PUNE”
GUIDENCE BY:DR. S.JAGTAP
PROF.SHREEDHAR.J
Name of the Student:Roll No.:-
A Report on Geological Site visit to
Marathwada Mitra Mandal College of
Commerce, Pune
20th March 2015: The Shetkari shikshan Mandals Bhivrabai Sawant College Of
Engineering ,Narhe, had organized a site visit to the campus of MMCC Pune to
study various types of Geological features formed million of years ago
The students departed from the college at 10:30 am and reached at the location
at 11 am where they were taken to the backside of the college to show various
types of geological formation. The student studied the evidences seen over their of
the various activities in the past. The subject geology studied by the Civil
Engineering students has a very significant role for the construction carried out in
Civil engineering as the base for the construction is the ground. A detailed study of
the ground is done so as to built a structure which is resistant to the activities of the
Earth like Earthquakes, Landslides etc. To predict such type of activities before it
occurs and produces a huge disaster to the human life. So it becomes significant to
study the history of the Earth which can be done by studying the evidences seen
on the surface or in the Earth surface.
Such subject needs a lot of practical knowledge this is achieved by actually
going to the site and study the Geology of the Earth. So as to attain the detailed
knowledge o f the Earths crust the Teachers of TSSM’s BSCOER Narhe
organized a site visit so that the students cam grasp more practical Knowledge
about the subject.
The features seen and studied by the students at the site are listed below and
elaborated further:
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Lava tube
Types of Lava & weathering effects
Various types of Joints
Silica Veins
Lava Tube
Lava Tube
What is a Lava Tube or Tunnel?
A lava tube is a natural conduit formed by flowing lava which moves beneath
the hardened surface of a lava flow. Tubes can be actively draining lava from
a volcano during an eruption, or can be extinct, meaning the lava flow has ceased
and the rock has cooled and left a long, cave-like channel.
Lava tubes are likely to exist on previously or currently geologically active planets
or moons, including the Earth.
How the Lava Tubes are formed?
Lava tubes are a type of lava cave formed when an active low-viscosity lava flow
develops a continuous and hard crust, which thickens and forms a roof above the
still-flowing lava stream. Tubes form in one of two ways: by the crusting over
of lava channels, and from Pahoehoe flows where the lava is moving under the
surface.
Lava usually leaves the point of eruption in channels. These channels tend to stay
very hot as their surroundings cool. This means they slowly develop walls around
them as the surrounding lava cools and/or as the channel melts its way deeper.
These channels can get deep enough to crust over, forming an insulating tube that
keeps the lava molten and serves as a conduit for the flowing lava. These types of
lava tubes tend to be closer to the lava eruption point.
Further away from the eruption point, lava can flow in an un channeled, fanlike
manner as it leaves its source, which is usually another lava tube leading back to
the eruption point. Called Pahoehoe flows, these areas of surface-moving lava
cool, forming either a smooth or rough, ropy surface. The lava continues to flow
this way until it begins to block its source. At this point, the subsurface lava is still
hot enough to break out at a point, and from this point the lava begins as a new
"source". Lava flows from the previous source to this breakout point as the
surrounding lava of the Pahoehoe flow cools. This forms an underground channel
that becomes a lava tube.
A broad lava-flow field often consists of a main lava tube and a series of
smaller tubes that supply lava to the front of one or more separate flows.
When the supply of lava stops at the end of an eruption or lava is diverted
elsewhere, lava in the tube system drains down slope and leaves partially
empty cave-like conduits beneath the ground.
Such drained tubes commonly exhibit step marks on their walls that mark
the various depths at which the lava flowed, known as flow ledges or flow
lines depending on how prominently they protrude from the walls. Lava tubes
generally have Pahoehoefloors, although this may often be covered in
breakdown from the ceiling. A variety of speleothems may be found in lava
tubes[3]including a variety of stalactite forms generally known as lavacicles,
which can be of the splash, shark tooth, or tubular variety. Lavacicles are the
most common of lava tube speleothems
Ripple marks forming Ropy structure
Pahoehoe Lava
Types of Lava
Lava flows are one of the most common hazards produced by active volcanoes.
Here in Hawai`i, they may endanger property but seldom endanger people's lives.
The threat they pose is largely dependent on how the flow moves, which is in turn
determined by the properties of the lava and the landscape. The two main types of
lava, pahoehoe and aa, differ in various properties, such as crystal and gas bubble
content, as well as having slight differences in temperature. These properties, along
with the steepness of the underlying slope, determine the ease with which a lava
flow moves. Once cooled, pahoehoe and aa are easily identifiable by their
characteristic textures
Pahoehoe Lava
Pahoehoe has a smooth, billowy, ropy surface and has at times been likened to the
surface texture of a pan of chocolate brownies also spelled pahoehoe, is basaltic
lava that has a smooth, billowy, undulating, or ropy surface. These surface features
are due to the movement of very fluid lava under a congealing surface crust.
The Hawaiian word was introduced as a technical term in geology by Clarence
Dutton. A pāhoehoe flow typically advances as a series of small lobes and toes that
continually break out from a cooled crust. It also forms lava tubeswhere the
minimal heat loss maintains low viscosity. The surface texture of pāhoehoe flows
varies widely, displaying all kinds of bizarre shapes often referred to as lava
sculpture. With increasing distance from the source, pāhoehoe flows may change
into aa flows in response to heat loss and consequent increase in viscosity.
Pahoehoe lavas typically have a temperature of 1100 to 1200 °C.The rounded
texture makes Pahoehoe a poor radar reflector, and is difficult to see from an
orbiting satellite (dark on Magellan picture).
Aa Lava
For the Polynesian name for the brightest star, see Sirius. Aa (is one of three
basic types of flow lava. Aa is basaltic lava characterized by a rough or surface
composed of broken lava blocks called clinker. The Hawaiian word was introduced
as a technical term in geology by Clarence Dutton.[7]
The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult
and slow. The clinkery surface actually covers a massive dense core, which is the
most active part of the flow. As pasty lava in the core travels down slope, the
clinkers are carried along at the surface. At the leading edge of an Aa flow,
however, these cooled fragments tumble down the steep front and are buried by the
advancing flow. This produces a layer of lava fragments both at the bottom and top
of an aa flow.
Accretionary lava balls as large as 3 metres (10 feet) are common on aa flows. Aa
is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into ʻaʻā if it
becomes turbulent from meeting impediments or steep slopes.
The sharp, angled texture makes ʻaʻā a strong radar reflector, and can easily be
seen from an orbiting satellite (bright on Magellanpictures).
ʻAʻā lavas typically erupt at temperatures of 1000 to 1100 °C
Joints in the Rocks
Joints in the Rocks
Joint is a break (fracture) of natural origin in the continuity of either a layer or
body of rock that lacks any visible or measurable movement parallel to the surface
(plane) of the fracture. Although they can occur singly, they most frequently occur
as joint sets and systems. A joint set is family of parallel, evenly spaced joints that
can be identified through mapping and analysis of the orientations, spacing, and
physical properties. A joint system consists of two or more interlocking joint sets.
The
distinction
between
joints
and fault
shinges
on
the
terms visible or measurable which depends on the scale of observation. Faults
differ from joints in that they exhibit visible or measurable lateral movement
between the opposite surfaces of the fracture. As a result, a joint may have been
created by either strict movement of a rock layer or body perpendicular to the
fracture or by varying degrees of lateral displacement parallel to the surface (plane)
of the fracture that remains “invisible” at the scale of observation.
Joints are among the most universal geologic structures as they are found in most
every exposure of rock. They vary greatly in appearance, dimensions, and
arrangement, and occur in quite different tectonic environments. Often, the specific
origin of the stresses that created certain joints and associated joint sets can be
quite ambiguous, unclear, and sometimes controversial. The most prominent joints
occur in the most well-consolidated, lithified, and highly competent rocks, such
as sandstone, limestone, quartzite, and granite. Joints may be open fractures or
filled by various materials. Joints, which are infilled by precipitated minerals are
called veins and joints filled by solidified magma are called dikes.
Weathering of Rocks
Weathering is the breaking down of rocks, soil and minerals as well as artificial
materials through contact with the Earth's atmosphere, biota and waters.
Weathering occurs in situ, roughly translated to: "with no movement" , and thus
should not be confused with erosion, which involves the movement of rocks and
minerals by agents such as water, ice, snow, wind, waves and gravity and then
being transported and deposited in other locations.
Two important classifications of weathering processes exist – physical and
chemical weathering; each sometimes involves a biological component.
Mechanical or physical weathering involves the breakdown of rocks and soils
through direct contact with atmospheric conditions, such as heat, water, ice and
pressure. The second classification, chemical weathering, involves the direct effect
of atmospheric chemicals or biologically produced chemicals also known as
biological weathering in the breakdown of rocks, soils and minerals.[1] While
physical weathering is accentuated in very cold or very dry environments,
chemical reactions are most intense where the climate is wet and hot. However,
both types of weathering occur together, and each tends to accelerate the other. For
example, physical abrasion (rubbing together) decreases the size of particles and
therefore increases their surface area, making them more susceptible to rapid
chemical reactions. The various agents act in concert to convert primary minerals
(feldspars and micas) to secondary minerals (clays and carbonates) and release
plant nutrient elements in soluble forms.
Silica Veins
Formations of Silica Veins
In geology, a vein is a distinct sheet like body of crystallized minerals within
a rock. Veins form when mineral constituents carried by an aqueous
solution within the rock mass are deposited through precipitation. The hydraulic
flow involved is usually due to hydrothermal circulation.
Veins are classically thought of as being the result of growth of crystals on the
walls of planar fractures in rocks, with the crystal growth occurring normal to the
walls of the cavity, and the crystal protruding into open space. This certainly is the
method for the formation of some veins. However, it is rare in geology for
significant open space to remain open in large volumes of rock, especially
several kilometers below the surface. Thus, there are two main mechanisms
considered likely for the formation of veins: open-space filling and crack-seal
growth.The vein seen at the site was a silica vein
Conclusion
Attending such site visit was a knowledgeable experience. At around 3 o’ clock
we departed from the MMCC college.
Concluding the report we thank our respected teachers because of whom the site
visit was possible and their valuable guidance on the site.
Dr.Jagtap sir & Prof. Shreedhar sir