Module #11 - Earthquakes
INSTRUCTIONS FOR TODAY
1. Watch the following video: Video of the Day: The Haiti Earthquake of 2010. (30 minutes) - I would suggest watching it for the 2nd half of the period.
Be sure to make point form notes in your digital video journal. Please make sure this document is SHARED with Mr. Durk.
2. Read the following information below in Part 1: Background and Terminology. Follow all hyper-links to external websites for activities, demonstrations and videos (if applicable). Copy only KEY information (i.e. the highlighted terms) to your notebook (or in your google docs). You may work with a partner to do this as there are quite a few key terms and concepts to get down.
3. Complete Part 2: Case Study: Earthquakes (see below) and post onto the Discussion Board (using the LMS)
4. Complete Part 3: Virtual Earthquake Activity (see below) and complete. Send your certificate directly to Mr. Durk's email - ugcloud.ca.
Earthquake Triangulation Online Lab
DUE DATE: Before Module #12 (Tuesday April 8th)
Part 1: Background and Terminology
Please remember to record all definitions and content in your virtual notebook. Definitions can be found by clicking on highlighted words.
Scientists now have a fairly good understanding of how plates move and how such movements relate to earthquake activity. Most movement occurs along narrow zones between plates where the results of plate tectonic forces are most evident.
There are three main types of plate boundaries:
Divergent boundaries, where new crust is generated as the plates pull away from each other.
Convergent boundaries, where crust is destroyed as one plate dives under another.
Transform boundaries, where crust is neither produced nor destroyed as the plates slide horizontally past each other.
Divergent boundaries
Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Example: Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest.
Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. This
submerged mountain range, which extends from the Arctic Ocean to beyond the southern
tip of Africa, is but one segment of the global mid-ocean ridge system that encircles the
earth. The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimetres
per year (cm/yr), or 25 km in a million years. This rate may seem slow by human standards,
but because this process has been going on for millions of years, it has resulted in plate
movement of thousands of kilometres. Sea floor spreading over the past 100 to 200
million years has caused the Atlantic Ocean to grow from a tiny inlet of water between the
continents of Europe, Africa, and the Americas into the vast ocean that exists today.
Acknowledgements: Image provided byUSGS
The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia.
In East Africa, spreading processes have already torn Saudi Arabia away from the rest of the African continent, forming the Red Sea. The actively splitting African Plate and the Arabian Plate meet in what geologists call a triple junction, where the Red Sea meets the Gulf of Aden. A new spreading center may be developing under Africa along the East African Rift Zone. When the continental crust stretches beyond its limits, tension cracks begin to appear on the earth's surface. Magma rises and squeezes through the widening cracks, sometimes to erupt and form volcanoes. The rising magma, whether or not it erupts, puts more pressure on the crust to produce additional fractures and, ultimately, the rift zone.
East Africa may be the site of the earth's next
major ocean. Plate interactions in the region provide
scientists an opportunity to study first hand how
the Atlantic may have begun to form about 200
million years ago. Geologists believe that, if spreading
continues, the three plates that meet at the edge
of the present-day African continent will separate
completely, allowing the Indian Ocean to flood
the area and making the easternmost corner of
Africa (the Horn of Africa) a large island.
Acknowledgements: Image provided by USGS
Convergent boundaries
The size of the earth has not changed significantly during the past 600 million years, and very likely not since shortly after its formation 4.6 billion years ago. The earth's unchanging size implies that the crust must be destroyed at about the same rate as it is being created. Such recycling of crust takes place along convergent boundaries where plates are moving toward each other, and sometimes one plate sinks (is subducted) under another. The location where sinking of a plate occurs is called a subduction zone.
The type of convergence that takes place between plates, called by some a very slow "collision", depends on the kind of lithosphere involved. Convergence can occur between an oceanic and a largely continental plate, or between two largely oceanic plates, or between two largely continental plates.
Oceanic-continental convergence
The Pacific Ocean is home to a number of long, narrow, curving trenches thousands of kilometres long and eight to ten kilometres deep cutting into the ocean floor. Trenches are the deepest parts of the ocean floor and are created by subduction.
Off the coast of North America along the Aleutian trench, the oceanic Juan de Fuca Plate is pushing into and being subducted under the continental part of the North American Plate. In turn, the overriding North American Plate is being lifted up, creating the towering Western Cordillera mountains of British Columbia. Even though the Juan de Fuca Plate as a whole is sinking smoothly and continuously into the trench, the deepest part of the subducting plate breaks into smaller pieces that become locked in place for long periods of time before suddenly moving to generate large earthquakes. Such earthquakes are often accompanied by uplift of the land by as much as a few metres.
Oceanic-continental convergence also sustains many of the earth's active volcanoes, such as those in the Andes and the Cascade Range in the Pacific Northwest. The eruptive activity is clearly associated with subduction, but scientists vigorously debate the possible sources of magma: is magma generated by the partial melting of the subducted oceanic slab, the overlying continental lithosphere, or both?
Oceanic-oceanic convergence
As with oceanic-continental convergence, when two oceanic plates converge, one is usually subducted under the other, and in the process atrench is formed. The Marianas Trench (paralleling the Mariana Islands), for example, marks where the fast-moving Pacific Plate converges against the slower moving Philippine Plate. The Challenger Deep, at the southern end of the Marianas Trench, plunges deeper into the Earth's interior (nearly 11,000 m) than Mount Everest, the world's tallest mountain, rises above sea level (about 8,854 m).
Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved. The trenches are the key to understanding how island arcs such as the Marianas and the Aleutian Islands have formed and why they experience numerous strong earthquakes. Magmas that form island arcs are produced by the partial melting of the descending plate and/or the overlying oceanic lithosphere. The descending plate also provides a source of stress as the two plates interact, leading to frequent moderate to strong earthquakes.
Acknowledgements: All content graciously provided by USGS
Convergent boundaries
Continental-continental convergence
The Himalayan mountain range dramatically demonstrates one of the most visible and spectacular consequences of plate tectonics. When two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. The collision of India into Asia 50 million years ago caused the Eurasian Plate to crumple up and override the Indian Plate. After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights. Most of this growth occurred during the past 10 million years. The Himalayas, towering as high as 8,854 m above sea level, form the highest continental mountains in the world. Moreover, the neighbouring Tibetan Plateau, at an average elevation of about 4,600 m, is higher than all the peaks in the Alps except for Mont Blanc and Monte Rosa, and is well above the summits of most mountains in North America.
Transform boundaries
The zone between two plates sliding horizontally past one another is called a transform fault boundary, or simply atransform boundary. Most transform faults are found on the ocean floor. They commonly offset the active spreading ridges, producing zig-zag plate margins, and are generally defined by shallow earthquakes. However, a few occur on land, such as the San Andreas fault zone in California. This transform fault connects the East Pacific Rise, a divergent boundary to the south, with the South Gorda.
The San Andreas fault zone, which is about 1,300 km long and tens of kilometres wide in places, slices through two-thirds of the length of California. Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr. Land on the west side of the fault zone (on the Pacific Plate) is moving in a northwesterly direction relative to the land on the east side of the fault zone (on the North American Plate).
The earth's surface is broken into seven large and many small moving plates. All move an average of a few centimeters a year relative to one another. These three types of movement are recognized at the boundaries between each pair of these plates.
Part 2: Earthquake Case Study
Click on the following LINK. Please choose a different earthquake from your peers.
1. Research and Report on one major earthquake that has occurred in the last 100 years. Describe the type of plate boundary, type of fault, rating on the Richter scale and number of deaths. Explain whether you think this region was prepared or not prepared for an earthquake of this magnitude (and back up your stance with evidence). Describe what local and federal governments could do to prepare citizens in this specific regions for future earthquakes.
2. Include a link to one interesting and relevant video that students can watch to learn more about this major earthquake and the resulting consequences.
3. Watch two of the videos posted by one of your classmates and provide useful & relevant comments on each.
Part 3: Earthquake Online Lab
Complete the Virtual Earthquake Lab & Earthquake Triangulation Online Lab and submit your "certificate" to Mr. Durk via ugcloud to show that you have completed it for the 1st lab.