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GLY3163- Olympic Exam Study Guide
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GLY3163- Olympic Exam StudyGuide
The Crescent Formation rocks are largely basalts lava flows that were erupted on the
seafloor before being accreted to North America. - Answer True
All of the sediment transported by rivers and deposited on the Juan de Fuca plate is
subducted deep into the mantle. - Answer False
The Cascade Range and the Coast Range were formed by subduction of the Juan de
Fuca plate under North America. - Answer True
Why are the rocks of the Core Area younger than the rocks of the Crescent Formation
even though they are beneath the Crescent Terrane? - Answer The Core Area rocks
were thrust under Crescent Formation by faulting
The Siletzia Terrane is oceanic lithosphere that was attached to North America - Answer
True
Where is the Olympic National Park located? - Answer Northwest Washington
Quick facts about Olympic National Park - Answer - Highest amount of annual
precipitation in the U.S.
- Roughly 60 active glaciers on high slopes
- Temperate rain forest on lower part of lower western slopes
- Rain shadow keeps northeastern slopes dry
- Young sedimentary rocks with submarine lavas
- These rocks were scraped off the ocean floor by plate convergence and pushed into a
heap on the Olympic Peninsula
- Western shores exposed to violent and stormy surf
Glaciers actively erode resistant ______________________________________ rocks of the
Olympic massif. - Answer metamorphosed deep marine rocks
Geographic Setting of Olympic - Answer - Preservation for the habitat of the elk meant
some of the Olympic rainforest was also saved
- Trees in the rain forest includes : Douglas fir, Sitka spruce, giant western hemlock, and
red cedar
- Ferns, mosses, and smaller plants cover the forest floor
,- Higher up are forests made up of subalpine firs and alpine meadows
- Above the tree-line are bare ledges, glaciers, snowfields, and peaks of the massif
- Olympic Peninsula has snow-capped mountains
- Once inhabited by Makah Native Americans who whaled
- About 150 inches of precipitation per year
- Radial drainage from the high area near Mount Olympus (highest peak 7965 feet)
- Streams rush down narrow valleys between steep interfluves
- Glaciers can sometimes block drainage
The trees in Olympic usually range in height from __________ to __________ feet, and
some even reach __________ feet. - Answer 100 to 200, some as tall as 300 feet
Geologic Features of Olympic - Answer - Miocene rock only about 15 million years old
(western side of shore) turned vertical and upside down
- Most sedimentary rocks were deposited in the deep ocean on the basaltic oceanic
crust (some laid down on partly submerged continental rock which then rode on
oceanic crust as a microcontinent or terrane)
- When Juan de Fuca (eastward moving segment of oceanic crust) meets the North
American Plate (westward moving), the heavier basaltic oceanic crust is
subducted/overridden by the lighter one
- From the same process as stated above, after millions of years, marine sedimentary
rock is accumulated by being scraped off the subducting plate, folded, compressed,
and thrust downward or squeezed upward, fractured, then partially metamorphosed,
then sliced and uplifted (this kind of tectonic activity created the Olympic Mountains)
- These effects are seen in the more eastern part of the park due to the up-warping of
the North Cascade Range and creation of the northern Cascade volcanoes
- Piles of submarine basaltic lava are exposed on the Olympic Peninsula and erupted in
Eocene time at mid-oceanic spreading center
- Lava cooled underwater as either pillow lava or brecciated rocks, though some
solidified slowly in dikes and sills between sedimentary beds or within previously
erupted lavas
- Basalt was altered by hot saline brines and by forces of the overriding North American
plate
- Between pillow lava eruptions were few beds of fossiliferous red limestone deposited
on the ocean floor (fossils were Foraminifera)
, What is Foraminifera? - Answer Single celled protozoa that secrete calcite and whose
tiny shells can barely be seen without the help of a magnifying glass
Red color of rocks in the eruptions (pillow eruptions) are caused by what? - Answer Iron
leached out from the cooling lava by the hot sea water
What is associated with the iron in the rocks that are red? - Answer Manganese and
copper
Upper North Fork of the Skokomish River are had what kind of rocks? - Answer Red
limestones associated with pillow lavas
In figure 32.6 (page 544), there are large rocks that are very bumpy looking and a
grayish-brown color. Explain what is seen - - Answer Eocene pillow lavas from the basalt
horseshoe or Crescent Terrane along the Hurricane Ridge Road. They appear as
bulbous pillow forms because the lava is erupted underwater and quenches at the
lava-water interface
Most basalts cropped out in what kind of pattern? - Answer Horseshoe
Explain the horseshoe pattern of the basalts - Answer The horseshoe partly rings the
peninsula and the arc portion of it is on the east side and the arms extend westward
- This horseshoe shaped rock unit is named the Crescent Formation and is also referred
to as the " basaltic horseshoe "
The oldest rocks are at the _________________ of Hurricane ridge and the youngest are at
the ____________. - Answer oldest = summit
youngest = base
Fossils of Foraminifera in the red interbedded limestone were dated as
_____________________ age. - Answer Eocene
What is indicated by the red limestones being dated in the Eocene age? - Answer The
basalt lavas are Eocene, too
The Eocene basalts are from a stranded block of ____________________________________
that became stuck in and older subduction zone further east. - Answer oceanic Farallon
plate
What is the name of the stranded Farallon plate? - Answer Siletzia terrane and makes up
much of the basement rocks of western Washington, Oregon, and Vancouver Island
The sedimentary layers between the Crescent Formation and the western coast become
progressively _____________ from east to west due to being scrapped off the subducting
plate and accreted from below and at the front of an accretionary prism above the
_____________________. - Answer younger, Juan de Fuca plate
Series of plate tectonic events that lead to the jumble of rocks on the Olympic Peninsula
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