Modern Monuments (L26) Flashcards
what are the 3 main stages recognized in the development of Stonehenge?
the first version built at approx 3000 BCE (circular ditch with small pits called Aubrey Holes)
2500 BCE - blue stones instralled at the centre shape of a horseshoe
2300 BCE - 30 sarsen stones (slabs of hard -silica semented sandstone) vertically imbedded in the ground
What rock is most of the bluestones made out of?
intrusive igneous rocks called diabase
What problem is there when speculating that the bluestones were quarried in Wales and dragged to Stonhenge?
there is a 500 year time gap
What is a possible alternative to the Wales quarry hypothesis?
possible that during the last Ice Age, ice sheets could have transported diabase slabs from Wales to English coasts
What is the trillithon?
three-stone structure that formed through sarsen stones formed in a horseshoe arrangement and capped by horizontal lintels
What is the Slaughter Stone?
it is a flat stone in Stonehenge that has little pits in the surface with a rusty brown color
name comes from people believing that it was stones where sacrifices were carried out and thought that the hematite rust was actually blood of the victims
What is an interpretation of what the purpose of Stonhenge was?
One popular interpretation is that Stonehenge functioned as an ancient observatory
and the arrangements of standing stones in the final version of Stonehenge marks the positions of the moon and sun during diff times of the year
Where is Mount Rushmore made?
in the Black Hills - represent an upwarded structure underlain by very old mica schists dating back to the Proterozoic
How was Black Hills created?
about 60-70 million years ago, the batholith was uplifted and the overlying sedimentary rocks warped
erosion then removed sedimentary rocks in the central part, leaving slanted strata
What are the 3 rock types observed in the Black Hills?
Protoerozoic scihsts (oldest rocks)
Paleozoic/Mesozoic sedimentary rocks
overlain by flat-lying Cenozoic sedimentary rocks in turn overlies the titled strata
Why was the original site “The Needles” deemed unsuitable for carving?
due to the severe jointing
How was the carvings made on Mt Rushmore?
excess granite had to be removed by dynamite, creating the head shapes
then finer details were carved through honeycombing
then workers used a pneumatic drill with a special bit to smooth out the honeycomb marks
What is honeycombing?
the method involved the drilling of holes to specific depths into the vertical cliff surface and removing intervening rock between the holes with hammers and chisels
What is a reason CN Tower is a monument of modern significance?
CN Tower is made largely of concrete which is the modern material of choice for construction in today’s world
CN Tower is ______
one of the world’s tallest freestanding structures
What were the 2 reasons why CN Tower was originally built?
Toronto had a huge construction boom of creating large skyscrapers and this caused communications problems (bad signal) so put transmitters and receivers very high above the ground to resolve this
also the CN company wanted to demonstrate the strength of Canadian industry
How was the concrete shaft created?
slip forming - involves pouring concrete into a massive mould or “slipform” and jacking the mould upward in steps
Why is it good that the CN Tower is elastic and sways a bit?
b/c if the tower was completetly still, the top would be in danger of snapping off
What is Concrete?
a mixture of cement, sand, rock, water, and small amounts of additives
How are concrete and cement different?
concrete CONTAINS cement as a binding ingredient
What is Cement?
the abbreviation of the more correct name, “Portland Cement” and is fine grey powder
what are 2 raw materials used for cement production?
calcite and silica
How is cement made?
- the raw materials are measured into desired quantities and crushed in multiple stages into a fine powder
- the powder is then fed into a preheating tower and cooked (preheating stage)
- the pre-heated material is then fed through a rotary kiln that heats the mixture further
- then the calcium reacts with the silica and a clumpy substance called clinker comes out
- the clinker is cooled, mixed w a small amount of gypsum and milled into a fine powder
this fine powder is cement
What happens when you add water to cement?
the water reacts with the calcium silicate to produce needle-like crystals of calcium silicate hydrate and calcium hydroxide
How does cements hardening work?
the calcium silicate hydrate crystals form an interlocking network, and this is what gives concrete its strength when dry
What are other mterials that need to be added to create concrete?
aggregate meterial such as sand and gravel adds bulk to the concrete and workes as a filler
Why is there no shortages of ingredients for cement production in Ontario?
Ontario has lots of limestone and sandstone as large deposits of sand and gravel were deposited when these continental glaciers of the last ice age melted
What are eskers?
snake-like landforms left behind from accumulations resulting from retreated ice sheets and well-sorted sand and gravel were deposited from the subglacial rivers
Ultimately, what are the materials that made the CN Tower?
limestone, sandstone, shale from the Paleozoic bedrock of Ontario deposited plus the aggreagate that was deposited from the last ice age
