Oceanography Exam 1 Google Earth Activity
What is the epicenter?
The epicenter of an earthquake is the point directly above the focus on either the land surface or seafloor; the depth of an earthquake has nothing to do with water depth, but instead is the depth in the solid earth from epicenter to focus
How is the lithosphere split?
The lithosphere is broken up into a number of thin plates, which move on top of the asthenosphere (middle mantle)
Describe the relationship between the locations of most active volcanoes and locations of earthquakes:
The most active volcanoes are lined up along the same area and in the same pattern as the blue, red, and purple earthquakes. This means the more active volcanoes are located on or near where the deep earthquakes occur.
what is a volcano?
an opening in the Earth's surface through which melted rock (magma), volcanic ash and/or gases escape from the interior of the Earth.
Is crust being created or destroyed at this plate boundary (and other spreading ridges)
created
Is this plate boundary divergent, convergent, or transform?
divergent
Modern methods to measure bathymetry
multi-beam echo sounders that map a wide swath of seafloor, and satellite measurement of variations in sea level due to variations in gravitational pull over bathymetric features - sea level is slightly lower over low spots on the sea floor and slightly higher over high spots.
What does observing where earthquakes occur tell us?
observing where earthquakes occur, both horizontally and with depth, tells us something about where stress is concentrated, and also about the material properties of the earth.
The different colors of refer to the depths of the earthquakes. What color are the shallowest earthquakes? ________ The deepest?_______
orange, red
What does the Plate Tectonics Theory posit?
that the outermost layers of the Earth (the crust and uppermost mantle) make up the brittle lithosphere of the Earth
On average, which is oldest - the continents or the ocean basins?
the continents
Complete this chart (see handout if need)
In the vicinity of ridges. (Scan 1500km or so on either side) In the vicinity of trenches. (Scan ~1500 or so km on either side) Describe the depth or range of depths of earthquakes, and the distribution (symmetric or asymmetric?) Is there any pattern to the depth distribution? There seems to be a good amount of shallow earthquakes on the ridges. They tend to be symmetric and are either orange or yellow, meaning they have shallow depth. Shallow depth at ridges There seems to be a good amount of deep earthquakes on the trenches. They tend to be symmetric and are either purple, blue or red, meaning they are deep in their depth. Deep depth at marine trenches. Oceanic plate subducting, so earthquake happens on one side only, not on both sides like it does at ridges.
1. Focus on the northern Atlantic Ocean, near the east coast of the US and the northwest coast of Africa. How long ago did the northern Atlantic Ocean begin to open up or start spreading? Describe your reasoning.
It began to open up and start spreading about 140-150 million years ago. I say this because the darkest color out from the mid-Atlantic ridge between these two areas is dark blue, which corresponds with 140-150 million years ago. This would have the been the first time the plates began to move apart would be at this point.
1. Find the South American plate, the African plate, and the Mid-Atlantic Ridge that marks the boundary between them. What happens to the age of the seafloor as distance increases away from the Mid-Atlantic Ridge?
It gets older as you move further away
1. Using Google Earth, "fly to" Challenger Deep, the deepest place on Earth (once Google Earth gets you there, you may have to zoom out to see where you are). Where is it?
It is an oceanic trench in the Mariana Trench, which is located in the Pacific Ocean. Southwest of Guam, near Mariana Islands.
What are theses underwater mountain ranges called?
Mid-Ocean Ridges
Examine the Atlantic Ocean between North/South America and Eurasia/Africa. What do you notice?
Note that the deepest part is not in the middle; instead there is an underwater mountain range that runs down the middle of the ocean.
What kind of rocks can be broken during an earthquake?
Only rocks that are cold and brittle (the earth's lithosphere) can be broken in earthquakes
what will happen with those other rocks during an earthquake?
Rocks that are hot and ductile will stretch and deform slowly over time without breaking (the earth's asthenosphere) - and thus do not produce earthquakes.
Discuss the start of ocean floor mapping
Such mapping began in the 1930's but accelerated during World War II with the advent of submarine warfare. Princeton Geosciences Professor Harry Hess played a pivotal role; as captain of the USS Cape Johnson he used the ship's echo-sounder to "ping" the seafloor and measure depth as the ship traversed the Pacific Ocean between battles. After the war, this data led him to propose seafloor spreading, a process crucial to the development of the theory of plate tectonics.
Using earthquake depths as evidence, is the Earth's lithosphere thicker in the vicinity of ridges or in the vicinity of trenches? Justify your answer.
The Earth's lithosphere is thicker in the vicinity of ridges because the trenches due to their position on the tectonic plates are constantly being torn up by the magnitude of the earthquakes and is therefore thinner. The lithosphere is then thicker at the ridges, where there are lower magnitude earthquakes.
What is the asthenosphere?
The asthenosphere is solid, but flows plastically over geologic time scales. Plate interiors are relatively stable, and most of the tectonic action (earthquakes, volcanism) takes place where plates meet - where they collide at convergent boundaries, move away from one another at divergent boundaries, or slide past one another at transform boundaries
If Earth's lowest parts are not in the middle of the ocean, where are they?
The deep linear features, the lowest points on Earth, are called ocean trenches. Kind of start out at the shelf break
1. Challenger Deep reaches 11 km (36,000 ft) below sea level. Which is greater, the elevation of Mt Everest (see question 3) above sea level, or the depth of Challenger Deep below sea level, and by how much?
The depth of Challenger Deep by about 6,968 feet.
1. Did the northern Atlantic Ocean basin start opening at the same time as the southern Atlantic Ocean basin? How much older or younger is the northern Atlantic basin than the southern Atlantic basin? Describe your reasoning.
The northern Atlantic Ocean basin is older than the southern Atlantic Ocean basin. I can tell because the coloration on the two areas is significantly different. The north Atlantic Ocean is about 140-150 million years old, whereas the Southern Atlantic Ocean is about 110-120 million years old. This may indicate that during the splitting of the continents, Africa and North America split before Africa and South America.
1. Describe any patterns you see in the distribution of earthquake epicenters over the Earth's surface - do they form lines, arcs, circles or clusters? Are patterns connected or disconnected?
They seem to all be clustered around plate boundaries.
Are mountains randomly distributed on the continents, or do they tend to occur in particular patterns (clusters, linear chains, arcs, etc.)?
They tend to occur in a particular pattern, especially in North and South America they tend to be quite linear. The Andes follows the entire west coast of South America, and the Rocky Mountains in North America are linear as well on the west coast of the continent. In Europe and Asia, mountains tend to occur in clusters, and in Africa, mountains tend to be linear and clustered.
Find Mt. Everest, the highest point on earth. Zoom in enough to see the summit, then pan your cursor around to locate the highest point (elevations shows up in the status bar at the bottom, as long as View/Status Bar is selected):
_____8,848______meters
Where do earthquakes originate?
a point called the focus (or hypocenter) which is not at the surface of the earth, but instead at some depth within the earth
What is plate tectonics?
a unifying framework for understanding the dynamic geology of the Earth
What is an earthquake?
a vibration of Earth caused by the sudden release of energy, usually as an abrupt breaking of rock along planar fractures called faults.
1. On average, continental crust is 2 billion years old; the oldest rocks are 3.8 billion years old, and some of the grains in those rocks are even older. What is the age of the oldest seafloor? _________
about 130-140 million years old
