Monday, February 23, 2009

♥CRUSTAL PLATES♥

VOLCANOES

Volcanoes did not play an important role in the Scriptures. However, some scholars have theorized that some of the events documented in the Scriptures were due to the actions of volcanoes, usually catastrophic events, possibly the plagues in Egypt. They played a factor in forming the terrain since the Biblical territory of Bashan, the now famous Golan Heights, was formed by extinct volcanoes. But for our purposes we are interested in volcanoes for what they can possibly tell us about the age of the earth.

Hawaii Kilauea eruption

Hawaii, beautiful vacation land, land of peace and harmony, yet each island was born of tremendous heat and violence. The long chain actually starts with Loihi seamount which is presently not visible since it is still approximately three thousand feet below sea level. It sprang to life again in 1996 and during the summer of 1996 the largest swarm of earthquakes ever recorded on ANY Hawaiian volcano shook Loihi seamount. The swarm began on 17 July 1996; to date, a total of over 5000 earthquakes have been recorded by the Hawaii Volcano Observatory (HVO) network. Does this mean that soon we will be seeing video clips on the TV news of a new island being born? Probably not, since many volcanologists propose that it will be thousands of years before Loihi becomes an island. Seabeam bathymetry images taken in 1997 show that where there had once been a 300 meter tall cone called Pele's Vents there was a new pit approximately 200 meters deep that has been named Pele's Pit.

Loihi 1997 seabeam bathymetry
(from http://www.soest.hawaii.edu/GG/HCV/loihi.html)
Next in the chain is Kilauea volcano, on the south side of the Island of Hawaii. It is one of the most active on Earth. Its current eruption (known as the Pu`u `O`o Eruption) started in January 1983 and as of January 2000 had produced 1.9 km3 of lava (0.112 km3/yr), had covered 102 km2, and had added 205 hectares to Kilauea's southern shore. In the process, lava flows unfortunately destroyed 181 houses and resurfaced 13 km of highway with as much as 25 m of lava. It has also destroyed a National Park visitor center and a 700 year-old Hawaiian temple ("Waha'ula heiau" before and after). There are no signs that the current eruption is slowing or will come to an end anytime soon.
Hawaiian Volcanoes

Kilauea shares the Hawaiian hot spot with its larger active sibling Mauna Loa and with Loihi seamount. Mauna Loa, or "Long Mountain" in Hawaiian, it rises 13,680 ft. (4,170 m) above sea level. USGS estimates are that due to the 33 recorded eruptions from January 10, 1843 to March 26,1984 on Mauna Loa it has added 4.124 km3 to the Hawaii landscape, a rate of only 0.029 km3 per year. However, Mauna Loa is a REALLY tall and big mountain. At 60 miles long and 30 miles wide, it makes up half of the entire island. When one considers that the flanks of Mauna Loa sit on sea floor that is about 16,400 ft (5,000 m) deep, the "height" of this volcano relative to neighboring land (the sea floor) is more like 30,080 ft (9,170 m)! Mauna Loa is the largest active volcano in the world. In fact, using this last measure of it's height, it is one of the tallest mountain in the world (although many mountains, such as Mt. Everest in the Himalaya mountain range, sit higher relative to sea level). Mauna Loa is a "shield volcano", which means it is a gently sloping mountain produced from a large number of generally very fluid lava flows.

Mauna Kea is the tallest mountain in the Hawaiian Chain. Its summit rises to an elevation of 4205m above sea level. It is the second largest in subaerial surface area of the five shield volcanoes that comprise the island of Hawaii, but is considered to be extinct. Also on the big island is Haulalai. The summit of Hualalai rises to an elevation of 2523m (8271ft) above sea level. The most recent eruption of 1800-1801 occurred along a northwest rift zone.

Other than the locations on Hawaii, the last volcano to be active was just to the west on Maui, Haleakala. It was last active in 1790, but could become active again at any time as world wide volcano history testifies. (for more on the Hawaiian volcanoes visit http://www.soest.hawaii.edu/GG/hcv.html)

Hawaiian chain
Hawaiian chain

However, the occupied islands of Hawaii that so many are familiar with is only a small part of the story as shown in the above figures. There is a long string of islands, coral atolls, and seamounts in a long chain that complete the picture. Each formed by volcanic action and modified over a long time by the forces of our wonderful planet. As one moves along the chain erosion and subsidence has taken its toll and the amount of exposed land area decreases dramatically, a testimony to the age progression along the chain. The extent of the coral deposits are relatively small around the occupied islands and progress until at Midway, where core drillings have been taken, there is a minimum of 820 feet (250 m) thick deposits and with limestone showing up to depths of around 1066 feet (325 m). The following figures show Nihoa island, Pearl & Hermes reef, and an animated depiction of the life of a volcanic Pacific island.

Nihoa Island Pearl & Hermes Volcano Life

The question is how could such an extensive chain of volcanoes be formed in a relatively short time? The most recent island building work of Kilauea of 1.9 km3 in 17 years is very inadequate. Kilauea is at a minimum 25,000 km3 or 6,000 miles3 in volume per the USGS. At the present rate it would take approximately 220,000 years to build the present volcano. However, evidence on the volcano indicate that it has not always produced flows at the present slow and relatively steady rate. Large and thick deposits of ash and pumice are present from older eruptions, reported in 1790 and again in 1924. Along the cliffs of the Hilina fault system are exposed 9 ash layers indicative of such eruptions, estimated to be thousands of years old (ref. http://geopubs.wr.usgs.gov/fact-sheet/fs132-98/).

Surtsey, Iceland from Nov. 8, 1963 to June 5, 1967 put forth an estimated 1 km3 to form the present volcano from a sea floor at 130 meters depth (ref. http://volcano.und.nodak.edu/vwdocs/volc_images/europe_west_asia/surtsey.html). Shown below are a photo and a map of Surtsey, note that some green growth has appeared, but only to a limited extent, and the erosion effects on the map. Some have predicted that unless there are more island building eruptions, Surtsey will no longer be seen above sea level in 100 years.

Surtsey, Finland Surtsey Map

Should Kilauea have grown continuously at the 1 km3 per 3.5 year rate it could have been built in 87,500 years.

Reportedly the greatest eruption of last century was in Katmai Alaska in 1912 (ref. http://wwwhvo.wr.usgs.gov/kilauea/) when an estimated ten cubic kilometers of pumice and ash was expelled. In recorded history possibly the Katmai eruption was surpassed only by Karakatau in 1883, Tambora in 1815, and Greece's Santorini eruption in ~1600 BC.(see Appendix A) The June 1912 eruption of Novarupta Volcano changed the Katmai dramatically. After the eruption 65 square kilometers (40 sq. miles) of lust green wilderness lay buried beneath hot pumice and ash, as much as 200 meters (700 ft.) deep in some areas. In near by Kodiak, for two days a person could not see a lantern held at arm's length. We don't know how much of the eruption was new material and how much was just relocation of material from the cone! (ref. http://volcano.und.edu/vwdocs/Parks/katmai/katmai.html).

Novarupta lava dome

If Kilauea could perform in this manner , output 10 km3 per year , it could possibly be built in 2500 years. However, there is definitely no evidence that such an occurrence could happened every year. See appendix D for indications in tree rings that the Hawaiian activity for the last 4000+ years has been relatively minor in nature.

And also don't forget, we need to build numerous volcanoes along the approximately 3045 mile long chain. The sister and elder volcano Mauna Loa, is much larger with a volume of 19,000 miles3 or 80,000 km3, more than three times the size of Kilauea. Many scientists believe that earlier in the Earth's history there were higher levels of volcanic activity, but the building of such an extensive chain of seamounts and islands in less than 10,000 years is difficult to visualize. Visualize, if you can, the crustal plate moving over the volcanic hot spot at a rate of 0.76 mile in a year, 8,025 times present max. rates, and volcanic material pouring forth at a rate greater than 188 cubic kilometers a year, 1,677 times present rate, assuming we need to build the equivalent of approximately 30 or more Kilauea's ( > 750,000 km3 ), in less than 4,000 years! Or even on a much smaller scale, building only Mauna Loa in less than 4,000 years would require average flow rates of 178.9 times the 17 year output rate of Kilauea!

We also need the appropriate amount of erosion, subsidence, and coral deposit development in such a relatively short time. The latest studies seem to indicate that the maximum rate of coral reef development is 21 meters per thousand years at optimum conditions. However, these studies indicate that coral reef development is not a continuous process. That sea temperatures, sea levels, water clearness, storms, pests and diseases are among the many factors that cause coral reef development to be an on again, off again process with mean reef growth values being between 1.3 and 4.2 meters per thousand years. (ref. http://cima.uprm.edu/~morelock/abstract/glynn30.htm ) For most coral to grow water must be relatively warm and shallow since energy from the sun is used in photosynthesis. Deep water blocks all sunlight and only very specialized corals can survive. Also should the coral start to develop while the volcano is still in the building stage, the newly developed coral formations may possibly be covered by new lava flows or ash and pumice. The 1993 "Hawaii Scientific Drilling Project" which drilled into Mauna Loa/Mauna Kea near the seashore hit a 85 feet (~26 m) thick deposit of "calcareous sediment" (coral reef deposit) after drilling through 100 feet of basalt. Possibly indicating 1,238 years of growth at the most optimum growth rate or around 20,000 years of growth at the slower 1.3 m/kyr growth rate. The above given reef growth rates also possibly indicate that if conditions were extremely optimum it would take at a minimum 11,905 years to build the coral reef deposit thickness at Midway. At the more reasonable 4.2 m/kyr development rate it would take 59,523 years to develop the 250 m thickness and this would start some time after the island building phase had slowed down and wave erosion had starting building the shallow shelves around the island necessary for extensive coral development.

Conclusion: The known physical characteristics of the volcanic Hawaiian Archipelago along with calculations based on known historic volcano performances presents a strong case against the formation of such an extensive chain in less than 10,000 years. Such a rapid formation would require crustal plate movement and volcanic material flows far exceeding known values for each parameter. Coral reef development speed would also seem to be a major problem. These indicators are proposed as strong evidence against a young earth, and strongly favoring an old age earth.


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Lake Varve Chronologies! Atmospheric Argon Where are the missing Isotopes?

Appendix A: USGS ratings of some historic eruptions.

Eruption volumes
(from http://pubs.usgs.gov/publications/msh/comparisons.htm)
USGS publishes an alternate rating of Katmai in http://vulcan.wr.usgs.gov/LivingWith/VolcanicFacts/ volcanic_impact.html, "Largest U.S. volcanic eruption of the 20th century, produced 21 cubic kilometers of volcanic material, which is equivalent to 230 years of eruption at Kilauea (Hawaii). (Or, about 30 times the volume erupted by Mount St. Helens in 1980.)" So be aware that as with most everything there are disagreements by different researchers as to the ratings of volcanic eruptions.

The ~1600 BC Santorini eruption has been estimated at 30-33 km3, after which the caldera collapsed into the sea. Submarine lava flows continued after the caldera collapse and were reported to emerge above sea level in 197 BC. Since then 11 recorded flow events have formed the Kameni Islands in the center of the caldera, with the last being in 1950. Though rising to 500 meters above the floor, only an estimated 2 km3 of the collapsed caldera has been refilled in about 3600 years. The Mount Mazama (now called Crater Lake, Oregon) eruption which the USGS has estimated at 42 km3 in ~5000 BC has also refilled to only a very limited extent. But even the larger of the above eruptions pales by comparison with the gigantic pyroclastic eruption evidences from volcanic systems such as Long Valley Caldera (California), Valles Caldera (New Mexico), and Yellowstone Caldera (Wyoming).

However, what would seem to be required to best build a long chain of volcanoes from the sea floor that extends for thousands of miles in length are not sudden violent eruptions. Especially if the sudden expulsion is followed by a collapse and it requires an extended time period for recovery as illustrated by Santorini and Mazama. The Hawaiian volcanoes, as are most volcanoes, are layered with ash interbedded within lava flows. The scientists of the 1993 "Hawaii Scientific Drilling Project" identified a minimum of 262 layers when drilling to 2460 feet(1056 m) into Mauna Loa/Mauna Kea. Around 80 percent of the layers were various forms of basalt, and the remaining layers interspersed within the basalt were characterized as coral(8), ash(15), soil(14), ash and soil mixed(10), and basaltic sand(5). (ref. http://expet.gps.caltech.edu/Hawaii_project.html) The below USGS "Simplified map of the Island of Hawai`i, showing the average rates of lava extrusion for historical eruptions on Mauna Loa (brown). The volcano is divided into four major sectors downslope from Moku`aweoweo caldera (shown in red): NER = northeast rift zone; MKS = Moku`aweoweo south; SWR = southwest rift zone; MKN = Moku`aweoweo north. In parenthesis, the rates of extrusion within each sector are in millions of cubic meters per day (6 = 6,000,000 m3/day). For comparison, the average rate of lava extrusion at Kilauea Volcano during the Pu`u `O`o eruption is less than 0.5 million cubic meters per day." (from http://wwwhvo.wr.usgs.gov/maunaloa/hazards/rate.html)

Moana Loa Estimated flow rates
Thus presenting USGS rough estimates of historic intermittent flow rates for Mauna Loa of 6, 12 and 24 times the rate of the present Kilauea Pu'u 'O'o eruption, well short of our estimated requirement of 1,667 times.

The known history of Santorini, Vesuvius and most others, indicates there is most often extended time periods of inactivity between layer building activity. Such extended periods of inactivity would greatly decrease the average yearly building rate for each volcanic island/atoll/seamount. The continuously active volcano is rare, such as Stromboli, which has been almost continuously active for a minimum of 2000 years, and some say 5000 years. But at Stromboli the large volume eruption or lava flow is very rare and therefore it has done relatively little building in recorded history. The USGS studies of lava flows on Haleakala is an illustration of the intermittent nature of volcanic activity, especially in the postshield stage, as shown below.

Haleakala crater lava flows
(from http://hvo.wr.usgs.gov/volcanoes/haleakala/cratermap_large.jpg)

Volcanos like Kilauea or Mauna Loa grow faster and erupt more frequently during the preshield and shield-building stages, when they are closer to the center of the hot spot. Possibly the recent history lava flow champ was at Laki, Iceland in 1783-1784 when 14.7 km3 was produced in 8 months. And near the same area, the Eldgja flow in ~935 put out 19.6 km3 in 3 to 8 years (the time is uncertain due to poor records). These flows in Iceland make a very good showing in the Greenland icecores due to their closeness to the drilling location. Recent studies have possibly identified evidences of much greater flow rates at the Columbia lava plateau, possibly 1300 km3 in 5 to 15 years, but these estimates are difficult to verify. The Columbia lava plateau consists of approximately 175,000 km3 of material from over 300 major flows and countless smaller flows. And even if the evidences for very high lava flow rates in the Columbia area are verified, the evidences are that there were also extended periods of inactivity. Therefore, the entire 175,000 km3 lava flow area was not developed in a short time period, but instead over a very extended time period. Scattered over the world there are many large igneous flow areas which give solid evidence of extreme activity in the past, some estimated at 10 times the size of the Columbia area, such as the Deccan Traps area of India.

Large Igneous Provinces

Appendix B: Hawaiian Legends of volcanic center movement

The possibility that the Hawaiian Islands become younger to the southeast was suspected by the ancient Hawaiians, long before any scientific studies were done. During their voyages, sea-faring Hawaiians noticed the differences in erosion, soil formation, and vegetation and recognized that the islands to the northwest (Niihau and Kauai) were older than those to the southeast (Maui and Hawaii). This idea was handed down from generation to generation in the legends of Pele, the fiery Goddess of Volcanoes. Pele originally lived on Kauai. When her older sister Namakaokahai, the Goddess of the Sea, attacked her, Pele fled to the Island of Oahu. When she was forced by Namakaokahai to flee again, Pele moved southeast to Maui and finally to Hawaii, where she now lives in the Halemaumau Crater at the summit of Kilauea Volcano. The mythical flight of Pele from Kauai to Hawaii, which alludes to the eternal struggle between the growth of volcanic islands from eruptions and their later erosion by ocean waves, is consistent with geologic evidence obtained centuries later that clearly shows the islands becoming younger from northwest to southeast. (from http://pubs.usgs.gov/publications/text/hotspots.html)

The Pele myths were associated with the genealogies of royal chiefs, with some genealogies extending back in time an astounding 95 generations. Some scholars believe that the occupants of the islands first arrived some time between 400 to 600 AD. And nearly all who study the history of the Hawaiians believe that they have occupied the islands for at least a minimum of 1000 years. Therefore the maximum possible time to be allowable for the forming of the west most occupied islands on which they would have first settled could be shortened by as much as 1600 years.


Appendix C: Pacific Atoll Drilling Results including Midway

Atoll drillings

Appendix D: TREE RINGS AND VOLCANOES

"Since the eruption of Mt. St. Helens and El Chichon in Mexico in 1982, there has been a renewed interest among scientists on a possible connection between large volcanic eruptions and significant effects on the climate. Some volcanoes inject sufficient material into the stratosphere that the amount of radiation received at the surface of the Earth from the Sun is materially altered. Large volcanic explosions deposit fine silicate ash and sulphur aerosols in the stratosphere, and these may remain there for some time.

Models of this type of event suggest that there would be an expansion of the region of circulating arctic air over western North America in January and a July weather pattern that would resemble those of a normal mid-May. One result of such weather would be to produce frosts in the height of the growing season in western North America.

Frost damage to mature trees is rare but can occur during the growing season with two successive nights at -5 C and days not above freezing. The freezing of water outside the immature growing cells crushes them and leaves a permanent record of frost in the tree ring for that year. In fact, the type of damage observed in the ring is different for the early part of the growing season and the late part. In a given tree ring, the date of the frost can sometimes be determined to within a week or two.

In several locations of the western United States lives the oldest known living thing on Earth: this is the Bristlecone pine (Pinus longaeva). In one location at Campito Mountain in the White Mountains of California, living trees and deadwood pieces provide an accurate year-by-year tree ring sequence back to 3435 BC, a continuous record for five and one-half thousand years! (Update: The bristlecone pine chronology in the White Mountains currently extends back almost 9,000 years continuously. That's to 7,000 BC! Several pieces of wood have been collected that will extend this date back even further. The hope is to push the date back to at least 8,000 BC. This will be important as the last Ice Age ended about 10,000 years ago, and to have a record of this transition period would offer scientists a wealth of information. (from http://www.sonic.net/bristlecone/dendro.html))

V. C. LaMarche and Katherine Hirsckboeck have recently reported, in the magazine Nature, on a study of the frost damage in the rings of the Bristlecone pine. In the recent tree-ring records, they find a remarkable correlation between frost damage rings and the known date of large eruptions. For example, in the past 100 years, there have been four climactically important events: Krakatoa (1883), Pelee, Soufriere (1902), Katami (1912), and Agung (1963). In each case, a ring of frost damage was found and always in the same year if the eruption was early in the year or, otherwise, the next year. The frost ring never preceded the volcanic event, which seems to prove that the frost rings are the result of the eruption.

When the tree ring record is examined back in time, there are some interesting results. Seventeen events are found in the rings between 2035 BC and 1884 AD. Some of these are known from other paleontological or historical evidence. For example, Mt. St. Helens erupted in 1500 AD and 2035 BC and Mt. Etna in 42 BC.

Of particular interest is the explosion of Santorini or Thera in the Agean Sea. This great explosion has been suggested as the cause of the decline of the Cretan civilization about 1450 BC. However, radio carbon dating of material found on Thera has given 1688 BC within an uncertainty of 50 years. (Update: reported on Athens News Agency, 12/03/2008, new precision radiocarbon dating of two recovered olive brances puts the catastrophe at 1613 BC, with an error margin of plus or minus 10 years (1603 to 1623)) Now the tree ring frost tells us that Santorini exploded in 1626 BC or, at most, one or two years earlier; i.e., about 275 years before the sudden decline of Crete, which thus still remains a mystery."
(from http://www.physics.uoguelph.ca/summer/scor/articles/scor23.htm)

The above indication that for 3919 years starting in 2035 BC there were only 17 significant world climate altering volcanic eruptions, many of which can be identified to a known historic eruption, is another way of saying in essence that during this time any above sea level activity in the Hawaiian Archipelago was by comparison of a relatively minor magnitude. And the Greenland icecores also tend to verify this conclusion. In other words, it is proposed that if over the last 4000 years there had been considerable above sea level activity in Hawaii of much greater magnitude than Laki or Eldgja, possibly up to 10 times or more, then there should have been many such indications in the records of the tree rings and/or strong showings in the Greenland icecore data.

♥SEAFLOOR SPREADING♥

Sea-Floor Spreading

Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.

Sea floor Spreading figure
(Fig 1.11) Sea floor Spreading.

As magma meets the water, it cools and solidifies, adding to the edges of the sideways-moving plates. As magma piles up along the crack, a long chain of mountains forms gradually on the ocean floor. This chain is called an oceanic ridge. The boundaries where the plates move apart are 'constructive' because new crust is being formed and added to the ocean floor. The ocean floor gradually extends and thus the size of these plates increases. As these plates get bigger, others become smaller as they melt back into the Earth in the process called subduction.

The new rock at the edge has no sediments like the sand or mud, since it is formed only recently. Farther away from the ridge, sand and mud gradually settle on it, in an ever-thickening blanket. The oldest rocks may have 14,000 feet of sand and other sediments resting on top of it.

An example of an oceanic ridge is the Mid-Atlantic Ridge. It is one part of a system of mid-oceanic ridges that stretches for 50,000 miles through the world's oceans. The underwater mountains of the ridge may not be more than two miles higher than the surrounding sea floor.

On the whole, sea-floor spreading is basically volcanic, but it is a slow and regular process, without the explosive outbursts of the volcanoes on land.

♥MID-OCAN RIDGES♥

Rift Zones

Image courtesy of: http://www.waterencyclopedia.com

Introduction

Throughout geological history the plates have been wandering about the globe. Fueled by geothermal processes deep within the mantle old ocean basins close up and new oceans emerge. Each time a plate is pulled apart it stretches the lithosphere. As the stretching continues rifts can occur. The continued pressure will eventually create a rift zone, and a new ocean basin is born. These rift zones are characterized by volcanism and are inundated with transverse faults. The record of magnetic anomalies on the Atlantic Ocean floor record the direction of propagation of the rifts. The information on the bottom of the Atlantic Ocean can be reconstructed to extrapolate the sequence of events of a rifting event.

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Driving Forces

The theory of plate tectonics describes the motions of the Earth’s many lithospheric plates. These plates are brittle pieces of lithosphere that sit and move on top of the mantle. The process is driven by convection of heat through the athenosphere. Lithospheric plates move in three motions relative to each other. Each motion creates a different type of plate boundary. The plates can either be moving toward each other (convergent boundaries), away from each other (divergent boundaries), or parallel to each other (transverse boundaries). Rift zones occur at plate boundaries where the plates are moving away from each other

This image shows the various types of plate boundaries. Image courtesy of: http://w3.salemstate.edu

The breakup of continental crust and the creation of new oceans basin begin at a rift zones. Mantle plumes, which bring up unusually hot material from deep in the mantle, have been documented at many rifting zones, although they are not essential for rifting to occur. These hot spots, however, may help speed along the rifting process in a variety of ways.

Hot spots cause a slight bulge in the overlying lithosphere (White and McKenzie 1989). In the early 1970s J . Tuzo Wilson of the University of Toronto and Kevin C. Burke and John E. Dewey from State University New York, Albany believed that the added stress from the bulging lithosphere may cause the apex of the continental dome to rupture in a three branched pattern resulting in two active rifts and one aborted rift (Courtillor and Vink 1983). In the 1980s Robert S. White and Dan P. McKenzie of the University of Cambridge conducted research that gave further evidence indicating hot spots are influential at many rift zones. Their research suggested that the added elevation of the lithospheric dome caused by the hot spot below the lithosphere helped to split the rift zone by way of increased gravity on either side of the rift (White and McKenzie 1989).

Lithosphere at divergent boundaries is stretched as the plate is being moved in different directions from conduction. As the divergent boundary is pushed in different directions the lithosphere stretches. With continual pressure from each side the lithosphere will eventually tear. Lithosphere tears in small patches along the line of most pressure. The rips are intermittent, and remain attached in some areas. These areas are referred to as “locked zones”. Despite the name, these zones do not prevent the ultimate failure of the lithosphere that lies between them. Eventually, the rifts elongate breaking the locked zone apart (Courtillor and Vink 1983).

In addition to the thinning of the lithosphere and upper mantle caused by stretching, the stretched plate is expected to subside over time. The North Sea is an example of lithosphere that has been stretched by approximately 35 percent and has subsided, creating a basin where much sediment has accumulated.

Image of the North Sea courtesy of: http://visibleearth.nasa.gov/

Upwelling of the lower mantle occurs under the stretched lithosphere which acts to further weaken the lithosphere (White and McKenzie 1989) The partial melting of the lower mantle creates volcanism of basaltic rock that is often rich in sodium and potassium. Basaltic lava is one of the geologic characteristics of rift zones (Burchfiel 1983).

Rifting occurs when the stretching does not stop. In some regions the continental lithosphere has been only been stretched a small amount before the stretching stops. If the stretching factor is near two, then limited upwelling that will result should cause little, if any, melting of the mantle. However, the lithosphere will still experience subsidence due to the stretching that did occur. According to seismic studies the final rupture comes once the lithosphere has been stretched beyond a factor of six (White and McKenzie 1989).

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Volcanism

Layers many kilometers thick often result from lava flow on to the thinned continental crust just after rifting occurs. The volcanic layers, which are basaltic in composition, are found on the edges of many continental margins. These layers are known to extend for lengths up to 2000 km along the coasts of Greenland, Scotland, Norway, the USA, South America, Africa, Indian, Antarctica, and Australia (White and McKenzie 1989).

The volume of magma that is released at these rift zones can be gigantic. The layers on the east coast of Greenland cover an area 2000 kilometers long, between four and 6 kilometers thick, and between 50 to 100 kilometers wide. That results in somewhere between one and two million cubic kilometers of rock produced at a single rift zone (White and McKenzie 1989)

The mid-ocean ridge is an example of a quiet rift volcano. Over much of the mid-ocean ridge magma is upwelled at nearly the same rate as the plates are spreading. Spreading along the mid ocean ridge occurs at a rate of anywhere from one centimeter to 20 centimeters per year (Bonatti and Crane 1984).

The temperature of the mantle has been recorded to have areas of unusually hot magma. If a rift opens over an area of hot mantle more of the lower mantle will melt as a result of decompression of the upwelling material. The raised mantle temperature will create larger volumes of melted mantle to be released after the rift has opened. More melting in rift areas will also cause a quicker reaction to the rift. Cooler magma will take longer to reach the surface after a rifting event has occurred than the hotter than average magma does (White and McKenzie 1989).

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Transverse Faults

The mid-ocean ridge is the largest known rift system on Earth. The mid-ocean ridge is not a continuous, straight line of underwater mountains. In many places it is offset laterally by a few to hundreds of kilometers. In fact, if you trace the Mid-Atlantic ridge you will find that offsets occur approximately every 50 to 100 kilometers. The smallest offsets are around 30 kilometers and can be much longer. The longer offsets usually have a trough and a ridge on each side that runs parallel to the trough. The ridges on each side are called transverse or transform ridges. The troughs and transform ridges are known as oceanic fractures zones. The zones are created from the stresses caused by the rifting process that creates new ocean basins (Bonatti and Crane 1984).

As the image above shows, the mid-ocean ridge system is composed of a series of short segments broken up by transverse faults. Image courtesy of: http://oceanexplorer.noaa.gov
This bathymetric map shows the extent of the mid-ocean ridge. Image courtesy of: http://oceanexplorer.noaa.gov
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Evidence

Magnetic anomalies locked in the rocks of the on the ocean floor provide evidence for plate tectonics and the rift zones. When new lithosphere is created the magnetic signature for the time is saved in the rocks. The varying magnetic signatures allow scientists to date the rocks according the magnetic signature of the time period. This gives scientists a way of dating the age of the ocean (Courtillot and Vink 1983). The newest ocean should be exactly at the mid-ocean ridge where new lithosphere is being created, and the oldest should be near the continents on either side of the ocean basin. The map created by the magnetic anomalies also show the path that the ocean took as it was rifting apart.

According to the magnetic anomalies, once a rift has started it propagates in a series of motions rather than in one uniform motion. The result is a jagged line that is continuous, but not linear. The transform ridges provide a temporary relief to the stresses put on a plate by the rifting process.

Magnetic anomalies on the ocean floor give evidence that rifts propagate in a nonlinear fashion. Two rifts at an angle to each other will be offset by a transform fault. When new oceanic crust is upwelled, and the center is spread, the tip of the southern rift propagates northward, transferring a block of the new ocean crust from east to west. The result is a wider ocean with a centerline that has zigzagged (Courtillor and Vink 1983).

In the Atlantic Ocean the Magnetic anomalies show that that the ocean opened up in discrete increments. According to the magnetic anomalies the South Atlantic ocean rifted first. The anomies indicate that the rift jumped from one oceanic fracture zone to the next. The rifting happened in right angles to the spreading (Courtillor and Vink 1983).

This image shows the corresponding magnetic anomalies in the oceanic lithosphere on either side of the mid-ocean ridge system. Image courtesy of: http://rst.gsfc.nasa.gov
Home Driving Forces Volcanism Transverse Faults Evidence Rifting References

Rifting Throughout History

When Pangaea was in existence in the late Paleozoic, South American and Africa were once fused along the western side of Africa and the eastern side of South America. Australia, India, and Antarctica were once located on the eastern side of Africa. North America was located on the northern tip of South American and the northwestern tip of Africa. And northern Europe was located to the east of North America (Dalziel 1995). Each time that a continent split away from the supercontinent a rift had to form and a new ocean basin was formed. The North Sea and the Red Sea are examples of rifting zones that are still in the early stages of rifting.

This seriers of images shows the breakup of Pangea over time unitl the continents reach their current day location. According to Continental Drift Pangaea began to break up approximately 225 million years ago. Image courtesy of: http://pubs.usgs.gov
Home Driving Forces Volcanism Transverse Faults Evidence Rifting References

References

Bonatti, Enrico, Kathleen Crane. “Oceanic Fracture Zones.” Scientific American 250/5 (1984): 40-51

Burchfiel, B. Clark. "The Continental Crust." Scientific American 249/3(1983): 130-142.

Courtillot, Vincent, Gregory E. Vink. "How Continents Break Up." Scientific American 249/1(1983): 42-49.

Dalziel, Ian W.D.. "Earth before Pangea." Scientific American 272/1(1995): 58-63.

Gilman, Larry. "Mid-Ocean Ridges." Water Encyclopedia. 2007. 23 Apr 2008 http://www.waterencyclopedia.com/images/wsci_03_img0352.jpg

"Phytoplankton Bloom in the North Sea." Visible Earth. 21 Apr 2008. NASA. 23 Apr 2008 http://visibleearth.nasa.gov/view_rec.php?id=3136

Redfern, Martin. "Drilling into a hot volcano." BBC news 26 Mar 2006 20 Apr 2008 http://news.bbc.co.uk/1/hi/sci/tech/4846574.stm

White, Robert S., Dan P. McKenzie. "Volcanism at Rifts." Scientific American 261/1(1989): 62-71.

Home Driving Forces Volcanism Transverse Faults Evidence Rift Examples References

Created by Susan June for ES767

April 24, 2008

♥INTENSITY OF AN EARTHQUAKE♥

Geoscape Canada

Geoscape Ottawa-Gatineau
Earthquakes
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Why do we have earthquakes?

The Ottawa-Gatineau region is located far from active tectonic plate boundaries, the usual source of earthquakes, but it does have a seismic history. Within this region, the Earth's crust is being compressed. Once the accumulated stress exceeds the strength of the crust, it is released by slippage along reactivated faults of the Ottawa-Bonnechere graben. Although this area has a moderate risk of a damaging earthquake, a devastating earthquake is unlikely.



What we feel

Magnitude (Richter scale), or size, reflects the amount of fault movement at the source of an earthquake. However, because the strength of shaking generally decreases with distance from the epicentre, what we feel and the amount of damage differ from place to place. Intensity is a measure of shaking at a specific place and ranges from I to XII (modified Mercalli scale). For any earthquake there will be one magnitude and many intensities.


Did you know?... On average, we feel an earthquake of intensity III or higher once every 3 years in Ottawa-Gatineau.

Ottawa-Gatineau was shaken into the year 2000 by a magnitude 5.2 earthquake centred at Kipawa, north of North Bay, about 300 km from Ottawa. In Ottawa, this event had a felt intensity of III.




Protecting ourselves

By evaluating the local history of earthquakes and the local geology, seismologists can produce maps predicting maximum ground motion or intensity for a region. Seismological data are used to set our national building codes that specify the engineering design requirements for earthquake-resistant buildings.


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♥CONTINENTAL PLATES♥

All About Plate Tectonics:
Earth's Plates and Continental Drift

The Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed. This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle.

The plates are made of rock and drift all over the globe; they move both horizontally (sideways) and vertically (up and down). Over long periods of time, the plates also change in size as their margins are added to, crushed together, or pushed back into the Earth's mantle. These plates are from 50 to 250 miles (80 to 400 km) thick.

Continental Drift
Forward Backward
Key

The map of the Earth is always changing; not only are the underlying plates moving, but the plates change in size. Also, the sea level changes over time (as the temperature on Earth varies and the poles melt or freeze to varied extents), covering or exposing different amounts of crust.

Earth's Major Plates:


The current continental and oceanic plates include: the Eurasian plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American plate, Caribbean plate, South American plate, African plate, Arabian plate, the Antarctic plate, and the Scotia plate. These plates consist of smaller sub-plates.

Earth's Crust

PLATE TECTONICS
Type of Crust Average Thickness Average Age Major Component
Continental Crust 20-80 kilometers 3 billion years Granite
Oceanic Crust 10 kilometers Generally 70 to 100 million years old Basalt
The theory of plate tectonics (meaning "plate structure") was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon.

The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the Earth's seismic activity (volcanoes and earthquakes) occurs at the plate boundaries as they interact.

The top layer of the Earth's surface is called the crust (it lies on top of the plates). Oceanic crust (the thin crust under the oceans) is thinner and denser than continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.

Under the crust is the rocky mantle, which is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. The upper mantle is rigid and is part of the lithosphere (together with the crust). The lower mantle flows slowly, at a rate of a few centimeters per year. The asthenosphere is a part of the upper mantle that exhibits plastic properties. It is located below the lithosphere (the crust and upper mantle), between about 100 and 250 kilometers deep.

TYPES OF PLATE MOVEMENT: Divergence, Convergence, and Lateral Slipping
At the boundaries of the plates, various deformations occur as the plates interact; they separate from one another (seafloor spreading), collide (forming mountain ranges), slip past one another (subduction zones, in which plates undergo destruction and remelting), and slip laterally.

Divergent Plate Movement: Seafloor Spreading
Seafloor spreading is the movement of two oceanic plates away from each other (at a divergent plate boundary), which results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle) along a a mid-ocean ridge. Where the oceanic plates are moving away from each other is called a zone of divergence. Ocean floor spreading was first suggested by Harry Hess and Robert Dietz in the 1960's.
Convergent Plate Movement:
When two plates collide (at a convergent plate boundary), some crust is destroyed in the impact and the plates become smaller. The results differ, depending upon what types of plates are involved.
Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a relatively light, thick continental plate, the oceanic plate is forced under the continental plate; this phenomenon is called subduction.
Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity.

Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.
Lateral Slipping Plate Movement:
When two plates move sideways against each other (at a transform plate boundary), there is a tremendous amount of friction which makes the movement jerky. The plates slip, then stick as the friction and pressure build up to incredible levels. When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.


ALFRED WEGENER AND PANGAEA
In 1915, the German geologist and meteorologist Alfred Wegener (1880-1930) first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core. The fossil record supports and gives credence to the theories of continental drift and plate tectonics.

Wegener hypothesized that there was an original, gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth". Pangaea was a supercontinent consisting of all of Earth's land masses. It existed from the Permian through Jurassic periods. It began breaking up during the Jurassic period, forming continents Gondwanaland and Laurasia, separated by the Tethys Sea.

LaurasiaPangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, the continents were separating into land masses that look like our modern-day continents.

Wegener published this theory in his 1915 book, On the Origin of Continents and Oceans. In it he also proposed the existence of the supercontinent Pangaea, and named it (Pangaea means "all the land" in Greek).

Fossil Evidence in Support of the Theory

Eduard Suess was an Austrian geologist who first realized that there had once been a land bridge between South America, Africa, India, Australia, and Antarctica. He named this large land mass Gondwanaland (named after a district in India where the fossil plant Glossopteris was found). This was the southern supercontinent formed after Pangaea broke up during the Jurassic period. He based his deductions on the plant Glossopteris, which is found throughout India, South America, southern Africa, Australia, and Antarctica.

Fossils of Mesosaurus (one of the first marine reptiles, even older than the dinosaurs) were found in both South America and South Africa. These finds, plus the study of sedimentation and the fossil plant Glossopteris in these southern continents led Alexander duToit, a South African scientist, to bolster the idea of the past existence of a supercontinent in the southern hemisphere, Eduard Suess's Gondwanaland. This lent further support to A. Wegener's Continental Drift Theory

Glossopteris, a tree-like plant from the Permian through the Triassic Period. It had tongue-shaped leaves and was about 12 ft (3.7 m) tall. It was the dominant plant of Gondwana.


ACTIVITIES ABOUT EARTH'S CONTINENTAL PLATES AND CRUST
An interactive quiz about plate tectonics
A quiz about Continental drift and plate tectonics
Label the outer layers of the Earth
Label Seafloor Spreading (Plate Divergence) Label the growth of new oceanic crust as two plates diverge.

Label Subduction (Plate Convergence) Label the desctruction of crust as two plates converge.

The Ring of Fire

WEB LINKS ON THE EARTH'S CONTINENTAL PLATES

The Great Continental Drift Mystery from the Yale-New Haven Teachers Institute, by Lois Van Wagner.
Questions and answers about continental drift from Monash University Earth Sciences.
Plate tectonics from the University of Tennessee (Knoxville).
Speed of the continental plates from Zhen Shao Huang.
Plate tectonics from the US Geological Service


The Planets Zoom Astronomy
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