Mountain Building - Orogenesis

Archimedes’ principle

Fig. 6.28

– The mass of the water displaced by the block of material equals the mass of the whole block

– Thus for a material with a lower density than water, the proportion of material above the water surface is constant

– For example wood (density 0.8 gm/cm) will have 20% of its mass above water (density of 1.0 gm/cm). Thus for a 1 m block 0.2 m will be above water and 0.8 m below, but for a 2 m block .4 m will be above water and 1.6 m below

Isostasy & Mountain Roots

Fig. 6.29

– Continental Crust has “roots”

– As a result of isostacy, the thicker the surface exposure of rock, the thicker the crustal “roots”

– As continental crust is compressed it shortens and thickens

– Avg. continental crust is 35-40 km thick, under deformed crust avg. is 50-70 km, with the majority of the difference in the “roots”

Fig. 6.31

Isostasy & Mountain Roots

Mountain-Types

• Fault-Block Mountains– Formed from tensional

stress

– Normal Faulting

– Example: Basin and Range Provinces SW USA

Mountain-Types

• Upwarped Mountains– Formed from compressional stress– Broad arching of the crust or great vertical displacement

along faults– Example: Black Hills SD

Mountain-Types

• Folded Mountains– Formed from compressional stress

– Reverse Faulting and Folding – highly deformed rocks

– Will have highly metamorphosed rocks

– Example: Appalachians, Himalayas

Mountain-Types • Volcanic Mountains– Formed volcanic activity

– Associated with plate boundaries or hot spots

– Example: Cascade Mts. Or mountains within Japan

Mountain Building (Orogenesis) Zones

Convergence ZonesContinental CollisionContinental Rifting

Convergence Zones

• Oceanic-Continental– Folded Mt. Belts– Thrust Faults– Volcanic Chains– Accreted Terranes– Example: Andes Mountains,

Cascades

Accreted Terranes• As exotic blocks collide

with continents they become sutured to the continent.

• The blocks are referred to accreted terranes

• Accreted Terranes are island arcs, portions of ocean floor, fragments of continental crust

Convergence Zones

• Oceanic-Oceanic– Volcanic Chains– Examples:

Japan, Philippines

Collision Zones

• Folded Mt. Belts

• Thrust Faults

• Remnants of Volcanic Chains

• Examples: Alps, Himalayas

Continental Rifting• Fault-block mountains

Mountain Building – Multiple Events

Example: Appalachian Mountains

Mountain Building, Rock Cycle and Plate Tectonics

Why does the Earth have mountains of

various height?• Erosion attacks

mountains – remember Earth wants to be flat

• Orogenic collapse.

Types of arial photographyaerial photography have been

classified on the basis of-1-direction of the camera axis

2-combination of more than one photograph

3-according to angle of coverage4-on the basis of colour

On the basis of direction of camera axis

1-vertical photographs2-horizontal or terrestrial

photographs3-oblique photographs

Vertical photographsa vertical photograph is taken

with the camera phinted as straight down as possible.

Allowable tolerance is usually +3 degree from the perpendicular

(plumb) line to the camera axis.A vertical photograph has the

following characteristics.1-the lens axis is perpendicular to

the surface of the earth.2-it covers a relatively small area.

3-the shape of the ground area covered on a single vertical photo closely approximates a square or

rectangle.4-being a view from above, it

gives an unfamiliar view of the ground

5-distance and direction may approach the accuracy of maps if

taken over flat terrain.6-relief is not readily apparent

Terrestrial photograph1-tehse are taken with photo-

theodolites from camera station on the ground.

2-these are used for survey of structures and mounments of

architectural or archaeological value.

Oblique photographs1-aerial photographs taken with

the optical axis of the aerial camera tilted fro, the vertical

2-these photographs cover large areas of ground.

3-but the clarity of details diminishes towards the far end of

the phothgraph.

Low oblique1-this is a photograph taken with

the camera inclined about 30 degree from the vertical

2-it is used to study an area before an attack, to substitute for a reconnaissance, to sustitute for a map, or to supplement a map.A low oblique has the following

characteristics –1-it covers a relatively small area.

2-the ground area covered is a trapezoid, althouth the photo is

square or rectangular.3-the objects have a more

familiar view, comparable to viewing from the top of a a high

hill or tall building.4-no scale is applicable to the

entire photograph, and distance cannot be measured.

Parallel lines on the ground are not parallel on this photograph,

therefore, direction (azimuth) can not be measured.

5-relief is discernible but distorted.

6-it does not show the horizon.

High obliquethe high oblique is a photograph taken with the camera inclined

about 60 degree from the verticalit has a limited military

application, it is used primarily in the making of aeronautical

charts.However, it may be the only

photography available.A high oblique has the following

characteristics.1-it covers a very large area (not

all usable)2-the ground area covered is a trapezoid, but the photographis

square or rectangular.3-the view varies from the very

familear to unfamiliar, depending on the height at which the

photograph is taken.4-distances and directions are not measured on this photograph for the same reasons that they are not

measured on the low oblique.5-relief may be quite discernible but distorted as in any oblique

view. The relief is not apparent in a high altitude, high oblique.

6-the horizon is always visible.

On the basis of combination of more than one photograph1-convergent photographs-

these are low oblique photographs taken with two

camera exposed simultaneously at successive exposure station, with their axis tilted at a fixed

inclination from vertical in opposite directions in the

direction of flight line so that the forward exposure of the first

station forms a stereopair with the backward exposure of the

next station.

2-trimetrogon photography-1-it is a combination of vertical and two oblique photographs in which the central photograph is

vertical and the side ones are oblique.

2-this photography can be used for rapid production of

reconnaissance maps on small scales.

Classification according to angle of coverage-

the angle of coveage is defined as the angle, the diagonal of the

angle, the diagonal of the negative format subtends at the rear node of the lens or the apez angle of the cone of rays passing through the front nodal point of

the lens.1-standard or normal angle photography- the angle of

coverage is of the order of 602-wide angle photography-the angle of coverage is of order of

90/3-super wide angle-the angle of

coverage is of order of 120.4-narrow-anlge photography- the angle of coverage is less then 60.

Classification on the basis of colour-

1-Black and White (panchromatic)

-these photographs are most commonly used for interpretation

and photogrammetry-images on these photographs is

similar to natural view but colour is restricted to shades of grey.

True colour--these photographs present the objects as they appear in their

natural colour.-for good colour cintrast, scale larger than 1:25000 is normally

used.-it has better in terpretation

capabilities.-it is better ofr photogrammeric

studies.-it is more useful in geological

mapping.It is expensive.

-prolinged preservation requires special care.

Infrared-this film has advantage of

recording information which the panchromatic film is not able to

do.-infrared raiaions which are invisible to human eye have

wavelengths ranging from 0.7 um to about 1.6um.

-infrared photography can be black and white or in colouir depending on the type of film

used.

Infrared colour--infrared colour4 photographs

shows vegetation in various hues of red.

-the differentiation between types of healthy and unhealthy

vegetation is brought out in distinctive colours.

-infrared colour with the combination of panchromatic

capabilities.

Infrared black and white--these photographs have the image in bleck and white.

-the vegetation which appears in dark tones on the panchromatic photography appears in lighter

tones on ir black and white photographs.

-water appears dark in ir black and white because water has high

absorption characteristics in infrared.

Yellow filter is used to reduce haze.

Multiband--in multispectral photography using blue, green, red, and ir

filters the same ground scene is photographed ot produce 4 black

and white negatives-the film used in iR black and

white negatives.-dispositive are made from the

negatives and the four images are combined in registration in an

additive colour viewer to produce a true colour or a false colour

viewer to produce a true colour or a false colour image on a

screen which can subsequently be photographed.