Download Folding and Faulting

Rocks of the earth’s crust are
folded and faulted by forces
within the earth
 Name
the parts of a fold and draw the main
types of fold.
 Discuss how folding has shaped the landscape
of Southern Ireland.
 Explain what a fault is.
 Explain and give Irish and international
examples of some of the landscapes associated
with faults.
 Describe the landforms created by folding and
faulting of the earth’s crust.
 The
same forces that move the plates also place
huge pressure on the rocks of the earth’s
surface.
 When rocks are crumpled up by these forces
they are said to be folded.
 Folds are easily seen in sedimentary rocks.
 Rocks can be folded because at depth they are
subjected to great heat and pressure which
allows them to bend without breaking.
 Different folds are created depending on the
strength and direction of the pressure put on
the rocks.
1
– Caledonian folding – 400 million years ago.
• Mountain ridges trend from northeast to southwest.
Eg Leinster mountains and Northwest Ireland.
2
– Armorican folding – 300 million years ago.
• Mountain ridges trend from east to west. Eg Munster
ridge and valley province.
3
– Alpine folding – 50 million years ago.
• Mountain ridges trend from east to west eg Alps and
Himalayas.
 Caledonian
Fold Movement occurred 400mya.
 The Eurasian and American Continental plates
collided during this period leading to the
formation of fold mountains.
 Pressure was exerted from the west so
mountains formed are in a North-South trend.
 The collision caused large amounts of
Connaught and Leinster to buckle and
wrinkle.
 Led to the formation of the Nephin Beg
Mountains and Maumturk Moutains in the
West.
 The
Dublin-Wicklow Mountains and Leinster
Batholith formed in the East during this
period.
 These mountains would have been as high as
the present day Alps but have been reduced
down to present height due to weathering and
erosion.






Armorican Fold Movement occurred over 250mya.
The Eurasian and African Continental plates
collided during this period leading to the formation
of fold mountains.
Pressure was exerted from the South so mountains
formed are in a West-East trend.
The collision caused large amounts of Munster to
buckle and wrinkle.
Led to the formation of Munster Ridges and Valleys
These mountain ranges were not as high as the ones
formed during the Caledonian folding as Ireland
was further away from the plate boundaries in
collision.
 Munster
Ridges & Valleys
 Between 350 and 400 million years ago huge
amounts of sand were deposited in the south and
southwest of Ireland.
 Today known as Old Red Sandstone.
 Later, a muddy sea covered the area and limestone
was laid down.
 300 millions years ago, Ireland’s rocks were
squeezed by earth movements, creating fold
mountains.
 These mountains stretch from Waterford to Kerry.
 Anticlines (ridges) – Comeraghs, Silvermines and
Galtee Mountains. The softer limestone that once
covered them has eroded away leaving sandstone
mountain ridges, but the synclines are still covered
with this limestone and form broad valleys running in
an East-West direction.
 The Blackwater Valley is an example. The River Lee
runs through a valley created during this period also
 Caledonian
– Highlands of Scotland
formed during this time
 Armorican – The Pyrenees in Southern
France were formed during this time.
 Alpine – occurred 60m years ago.
Eurasian and African Plates collided. Did
not affect Ireland as we were too far prom
point of collision. Mountain ranges such
as the Alps and the Appenine Moutains
formed.
 Himalayas, the
origin of the Himalayas is the
impact of the Indian Tectonic Plate travelling
northward at 15 cm per year to impact the
Eurasian continent, about 40-50 million years
ago.
 The movement continues and as a result the
mountains increase in height by about 5mm
each year.
 Andes Mountains – formed due to the collision
of the Pacific Ocean plate and the South
American continental plate.
 Near
the surface of the earth rock is
brittle and will crack or fracture when
placed under great stress by earth
movements.
 Rocks contain small fractures or joints,
but where a lot of movement has
happened along a fracture, it is called a
fault.
 When
a sloping fault is created and land
slips down along one side of it.
 These are caused by the land being pulled
apart (tension), sometimes making a valley.
 If
pressure from earth movements
(compression) causes land to move up along
a sloping fault.
 Sometimes makes block mountains: eg The
Ox Mountains of County Sligo.
A
type of reverse fault where the angle of the
fault plane is very low
 Tear
faults (transform faults) occur where
there is a vertical fault in the landscape
but movement has been horizontal.
 Similar to the movement along the San
Andreas Fault in California.
 When
rocks of the earths crust are pulled
apart by movement of tectonic plates, they
often split. These cracks in the crust are
called faults.
 The first type of fault found in Ireland is a
normal fault.
 Crust can be stretched and thinned due to
forced within the earth. Eventually the rocks
fractures and the movement of land is
downwards.
 E.g. Near Kingscourt, Co. Cavan.
 The
second type of fault found in Ireland is a
reverse fault.
 These occur when rocks within the crust are
subjected to compression (at destructive
plate boundaries)
 The compression causes the rocks to fold
upwards.
 The rocks can only fold upto a certain point
before they fracture and the movement of
land is upwards.
 Eg. Fault running from Killarney to Mallow.
 Sometimes
faulting can lead to features
known as block mountains forming.
 E.g. Ox mountains in Connaught
 These features form when the land
between tow parallel faults is forced
upwards.
 Rift Valleys
are formed when a block of land
between sets of parallel faults slips down due
to stretching of the crust.
 A flat floored valley with steep sloping sides is
formed as a result.
 The steep slopes mark the fault lines and are
called fault scarps.
 Lough Neagh and the lower Bann valley occupy
such a rift valley.
 Larger rift valleys occur in the East African Rift
Valley.
 It is over 5000 km long and varies in width from
30-100kms.
 Dome
mountains are the result of a great
amount of melted rock pushing its way up
under the earth.
 The crust is heaved upward into a rounded
dome.
 Weathering and erosion attack the upland
formed by the dome, often exposing the
igenous rock at the heart of the dome
mountains.
 Common in North America, eg the Black
Mountains of South Dakota.
2006