Paper 1:
Introduction
The area of study is the Kurile trench, identified as a small
area on the class CDROM (Fig. 1).(1) This area
corresponds to a plate boundary thought to exist by geologists
between the Pacific plate and the Indo-Australian plate
(Segar, p.62). (2) The data collected supports the theory
of plate tectonics at a convergent plate boundary.(3)
Methods
The data includes topographical profiles created through the ETOP05
elevation dataset which consists of digital elevation data of
sea floor and land.(4) The sources for this
data come from: Ocean Areas-US Naval Oceanographic Office;
USA, W. Europe, Japan, Korea, US Defense Mapping Agency; Australia:
Bureau of Mineral Resources; New Zealand: Department of
Industrial and Scientific Research; US Navy Fleet Numerical Oceanographic
Center.(5) Gridded data varies in resolution
from 5 minutes latitude/longitude to 1 degree.(6) Earthquakes
are from USGS preliminary determination of epicenters and volcano
data are from the Smithsonian Institution Volcano database. (7)
Observations
Three
profiles taken along the coastal region of the Khamchatka Peninsula
display the topographic features of an oceanic trench (see Fig.
2 for profile locations).(8) Thousands of volcanoes
exist parallel to the trench and 200-400 km inland (Fig.2).(9)
The trench lies at 60 degrees N latitude and 160 degrees E longitude
and extends for 2,200 km in length along this coast.(10)
One profile displays the gentle upward slope of the Pacific Ocean
Basin which then becomes drastically altered by the sudden drop-off
of the trench (Fig.3).(11) Following the trench,
a virtual linear rise occurs as the profile moves northwest and
inland.(12) A second profile confirmed the presence
of the trench 500 km to the south of the first profile, but showed
a 400 km long basin located behind the vertical rise of the volcanoes.
(13) The basin dips 3,000 m below sea level (Fig.
4).(14) A third profile shows both the existence
of the trench another 250 km to the south and the land features
described by the first two profiles (Fig.5).(15)
Earthquakes'
foci were also plotted along the same path as the middle topographic
profile of the Khamchatka coast.(16) The plot shows
earthquakes occur consistently along this trench (Fig.6).(17)
A cross section of earthquake activity along the middle profile
shows a descending pattern of earthquakes to depths of 600 km
(Fig.7).(18)
Interpretations
In
this scenario, a plate containing oceanic crust collides with
a plate made of continental crust.(20)
One of
the plates descends beneath another, into the Earth's asthenosphere
(Figure .8).(21) A topographic trench is formed where one
of the plates begins its descent.(22) This process
is called subduction.(23) The sinking plate causes
a corresponding pattern of deep earthquakes along its boundary.(24)
Melting magma along the upper edge of the plate rises
to the surface, creating volcanoes.(25) Figure 9
shows a cross-section diagram across the middle profile, showing
the subduction model and observations of topography, quakes, and
volcanoes that occur in agreement with the model.(26)
Paper
2
Introduction
I will discuss the motions of the plates and their effecting result
on the sea floor and the Earth.(1) At the center
of my discussion will be the Mid-Atlantic Ridge and why it has
formed into an S shape.(2) It is an underwater mountain
range, also known as an oceanic divergent margin.(3)
Observations
The Mid-Atlantic Ridge is a very interesting part of our Earth.(4)
It is an underwater mountain range, also known as an oceanic divergent
margin.(5) This ridge runs north to south down the
center of the Atlantic from the North Pole to Antarctica.(6)
Many different plates meet at the ridge including the North American,
the Eurasian, the South American, and the African Plate.(7)
The ridge extends at one point as deep as 5,625 m below sea level.(8)
It stretches east to west from Europe and Africa to the east coast
of the Americas, 2,547 km.(9) This is evident in
Figure 1.(10)
An oceanic divergent margin means that the plates, which form
the Earth, meet and disperse in opposite directions.(11)
The resultant gap from these diverging plates is filled up with
uprooted, low density magma.(12) This process leads
to the series of volcanoes which form into a ridge in the gap
left by the plates.(13) This process is known as
sea floor spreading.(14) This is also illustrated
in Figure 1.(15) The aging crust then sinks steadily
down, while the mountains in the ridge slowly move outward while
new ones fill in their place.(16) The mountains move
in the direction of the plate.(17) This part of the
process, combined with narrowness of the Atlantic and the shape
of the continents, leads to the S shape formed by the ridge.(18)
Interpretations
My study shows the Mid-Atlantic Ridge is an oceanic divergent
margin that is formed in an S shape due to many different factors
including ocean size, plate motion, volcanic activity, and sea
floor spreading.(19) This is proven by the data gathered
from the map program and is reinforced by the area's topography,
which includes volcanoes and earthquakes.(20)
After you
are finished with the classification exercise, which paper do
you think presented the most effective argument? Can you tell
which paper is the most effective by the relative numbers of various
classifications of statements?
