Environmental Geology - Assignment Example

Environmental Geology Environmental Geology 25 pts) The M9.0 Great Tohoku earthquake, northeast Honshu, Japan that occurred on March11, 2011 caused widespread damage. Describe 1) the relative directions and magnitudes ofplate movement, 2) the frequency of earthquake occurrences in these regions, and 3) the causeand scale of the tsunami which followed the earthquake.Ans. (a) The magnitude 9.0 Tohoku earthquake on March 11, 2011, which occurred near the northeast coast of Honshu, Japan, resulted from thrust faulting on or near the subduction zone plate boundary between the Pacific and North America plates.

At the latitude of this earthquake, the Pacific plate moves approximately westwards with respect to the North America plate at a rate of 83 mm/yr, and begins its westward descent beneath Japan at the Japan Trench. Note thatsome authors divide this region into several microplates that together define the relative motions between the larger Pacific, North America and Eurasia plates; these include the Okhotsk and Amur microplates that are respectively part of North America and Eurasia.(b) The Japan Trench subduction zone has hosted nine events of magnitude 7 or greater since 1973.

The largest of these is a M 7.8 earthquake approximately 260 km to the north of the March 11 epicenter, caused 3 fatalities and almost 700 injuries in December 1994. In June of 1978, a M 7.7 earthquake 35 km to the southwest of the March 11 epicenter caused 22 fatalities and over 400 injuries. Large offshore earthquakes have occurred in the same subduction zone in 1611, 1896 and 1933 that each produced devastating tsunami waves on the Sanriku coast of Pacific NE Japan.(c) The coastline here is particularly vulnerable to tsunami waves because it has many deep coastal embayments that amplify tsunami waves and cause great wave inundations. The M 7.6 subduction earthquake of 1896 created tsunami waves as high 38 m and a reported death toll of 22,000. The M 8.6 earthquake of March 2, 1933 produced tsunami waves as high as 29 m on the Sanriku coast and caused more than 3000 fatalities.

The March 11, 2011 earthquake far surpassed other earthquakes in the southern Japan Trench of the 20th century, none of which attained M8. A predecessor may have occurred on July 13, 869, when the Sendai area was swept by a large tsunami that Japanese scientists have identified from written records and a sand sheet.2. (20 pts) Describe the geological setting and the main features of the 2010 eruptions ofEyjafjallajökull in Iceland. What were some of the hazards associated with this volcaniceruption?Ans. Eyjafjallajökull, also known as Eyjafjöll, lies south of the intersect between Icelands East Volcanic Zone (EVZ), a NE-SW trending rift system, and the E-W trending South Iceland Seismic Zone (SISZ).

The EVZ is currently the main zone of divergence between the North American and Eurasian plates on the Icelandic landmass, with slightly less divergence currently occurring at the parallel Western Volcanic Zone. Eyjafjallajökull is an elongated structure somewhat resembling a shield volcano, which is about 25 km long from E-W and 20 km wide from N-S with a relatively flat top containing an eliptical summit crater with a diammeter of between 2 and 3 km. Most of the fissures and crater rows are correspondingly E-W oriented.

The rim has three highpoints, known as Gudnnastein, Godastein and Hamundur, the latter being the summit at 1650 m elevation. The upper parts of the structure are relatively flat but the flanks are heavily eroded and drop off steeply at the edges. The summit crater and some of the surroundings are glaciated, with a maximum thickness of about 200 m, and the Gigjökull glacier extends from a breach in the north crater wall down to near the valley floor.The eruptions of the volcano caused major disruptions to aviation as ash from the eruption was transported with northwesterly winds towards Europe and the North Atlantic area.

This was the largest disruption of aviation since the Second World War, as airspace over large areas was closed for several days in April with delays and flight cancellations affecting millions of travelers around the world.3. (10 pts) Approximately two years ago (January, 2011) there was serious flooding inQueensland, Australia. What were the reasons for this flooding and was it typical for thisarea?Ans. The devastating floods in Queensland in Jan 2011 was a result of heavy rains caused by two normally independent weather phenomena, the L Nina and the annual monsoonal low pressure trough.

The La Nina is a periodic interaction between the Pacific Ocean and the Earth’s atmosphere causing trade winds drive warmer surface waters west to the coast of Australia resulting in cloud formation and heavy rainfall, while the monsoonal low pressure trough brings wet weather to the region. The confluence of the two independent events caused the unprecedented floods in the region and is not typical of this area.4. (25 pts) Calculate the water discharge of a river that has a cross-sectional area of 10 m2 and anaverage velocity of 2 m/s.

Assuming each m3 of water carries 1 g of sediment, calculate thetotal load of sediment carried by the river. If this sediment contains 30 ppm mercury, howmuch mercury is transported by the river? During a storm event the cross-sectional area of theriver increases to 50 m2 and the velocity increases to 20 m/s. What impact does this higherrate of flow have on mercury transport (what is the new mercury load)? For this calculation,assume the river flows through an isolated channel. Hint: ppm represents parts per million or1 mg/kg sediment.Ans. (a) Water discharge = Cross-sectional area * velocity = 10m2 * 2m/s = 20m3/s (b) Load of Sediment = Flow volume * Sediment/m3 = 20m3/s * 1g/m3 = 20g/s (also 20/1000 = 0.02 Kg/s) (c) Mercury carried = Load of Sediment * mercury ppm of sediment = 0.

02Kg/s * 30ppm = 0.6ppm (also 0.6mg/s) (d) Water Discharge during storm = 50m2 * 20m/s = 1000m3/s Load of Sediment during storm = 1000m3/s * 1g/m3 = 1000g/s = 1Kg/s New Mercury load carried = 1Kg/s * 30ppm = 30ppm (also 30mg/s)5. (10 pts) What is the difference between a gaining stream and a losing stream? How wouldinteraction with the subsurface influence the stream velocity calculated in question 4?Ans. Streams interact with ground water in all types of landscapes. When the interaction results in streams gaining water from inflow of ground water through the streambed, it is called gaining stream and when they lose water to ground water by outflow through the streambed, it is called losing stream.

For ground water to discharge into a stream channel, the altitude of the water table in the vicinity of the stream must be higher than the altitude of the stream-water surface. Conversely, for surface water to seep to ground water, the altitude of the water table in the vicinity of the stream must be lower than the altitude of the stream-water surface.The stream velocity would increase in gaining stream conditions while the velocity would decrease in losing stream conditions.6. (10 pts) Briefly describe why the mercury pollution at Grassy Narrows, Ontario is sopersistent?

See the following CBC news article from last summer:http://www.cbc.ca/news/canada/story/2012/06/04/grassy-narrows-mercury.html.Commercial fishing has been closed in the waters near Grassy Narrows First Nations now for over 40 years because of mercury poisoning from a paper mill, but its people are still suffering the effects. In 1969, it was revealed that the English-Wabigoon river system in Ontario, Canada had been contaminated with mercury emitted by a caustic soda factory located upstream.

The residents in the 2 Indigenous communities along the river near Kenora, Ontario were poisoned by eating fish contaminated with mercury. The complex river system makes it hard to distinguish which way the current runs and general opinion is that it would take 100 years for the water to reach the ocean. The river is very wide and the current is slow. Also, at least 7 tons of mercury was released into the river system. The huge quantity of mercury and the slow flow rate of water to the ocean have resulted in slow depletion of the mercury levels in the region.

Works citedConrad, Quilty-Harper. Australia floods: what caused the flooding? www.telegraph.co.uk, 12 Jan. 2011. Web. 10 Feb 13.Harada, M., et al. “Mercury Pollution in First Nations Groups in Ontario, Canada: 35 years of Canadian Minamata Disease”. Journal of Minamata Studies (2011): 3-30. Web. 09 Feb 13.International Volcanic Ash Task Force (IVATF). The 2010 Eyjafjallajökull eruption, Iceland, 15 Jan. 2012. Web. 09 Feb 13.US Geological Survey. Natural Processes of Ground-Water and Surface-Water Interaction, n.d. Web.

09 Feb 13.US Geological Survey. Poster of the Great Tohoku Earthquake (northeast Honshu, Japan) of March 11, 2011 - Magnitude 9.0, 14 March. 2011. Web. 09 Feb 13.