olelog

A new Journal has seen the light. The first issue of Journal of Flood Risk Management, a new publication for 2008, published jointly with the Chartered Institution of Water and Environmental Management (CIWEM) and Wiley-Blackwell is just (in the library and) on line.

With the recent cyclone flooding Myanmar in mind, that affected between 1.6 million and 2.5 million people with estimated death tolls that range from 68,833 and 127,990, the timing seems appropriate. With the way the military regime handles the situation, I fear that more deaths will follow from famine and disease. No doubt Myanmar is on the brink of a public health catastrophe.

Articles published in Journal of Flood Risk Management will be freely available to download in 2008. If interested click on this link to view articles from the first issue.

The most powerful earthquake to hit China in 30 years has killed at least 10,000 people in south-western Sichuan province, with thousands more trapped. The figures are expected to rise dramatically

The M 7.9 strong earthquake was shallow, with a depth of only 10 km, and hit less than 100 km north-east of Chengdu, a city of about 11 million inhabitants. The quake devastated a region of small cities and towns set amid steep hills. The epicentre was relatively far from any plate boundary, but earthquakes in this area are not unknown as can be seen from this USGS map of earthquakes from 1990 to present. Since 1900 the area of this map has known 8 earthquakes larger than M 7.

Kim at All of my Faults are Stress-related has an exellent post on the Tectonics of the May 12 Sichuan earthquake which explains the tectonic situation much better than I would ever be able to, so please go and read it.

The Eastern Sichuan quake ruptured about 275 kilometers of a fault running northeastward between the easternmost mountains of the Tibetan Plateau and the densely populated Sichuan Basin. The violent quake is probably linked to a shift of the Tibetan plateau to the north and east. Earthquakes are frequent and deadly along the fringes of the Tibetan plateau, which was raised when India collided into Eurasia, starting some 50 million years ago.

• http://sciencenow.sciencemag.org/cgi/content/full/2008/512/1?rss=1
• http://www.abc.net.au/science/articles/2008/05/13/2243183.htm



PS:
A strong aftershock measuring 6.1 on the Richter scale rocked Chengdu itself around 3:10 p.m. Tuesday 13 May 2008. The region has suffered more than 1,950 aftershocks in the past 25 hours, including three over 6 on the Richter scale and 14 between 5 and 6. Heavy rainfall, storm and wrecked roads hamper rescuers' efforts to reach the hardest-hit areas.

PS of 14 may 2008
More about the earthquake including information (and Tectonic Summary) as Reported by USGS at Geology.com

Over 30 people have been killed this month and hundreds more injured as ‘norwesters’, wreaked havoc across Bangladesh.

Nor'wester thunderstorms, locally known as Kal-baishakhi, often blow over Bangladesh in April-May from a northwesterly direction. Nor'wester thunderstorm coincides with the setting in of the summer season. From mid-March to April the temperature in Bangladesh rises sharply compared to the preceding months (i.e. winter months). In the middle of April the whole country, especially the northwestern part, records a sharp rise in day temperature. Presence of warm and moist air in the lower layer of the atmosphere is an essential precondition for the development of a nor'wester.

The main reasons behind the nor'wester is the warm and moist air coming from the southeast which rises up to 2 kilometres, mixes with the relatively cold and dry jet streams coming from the northwesterly and westerly directions. The mixing of these two dissimilar air masses causes storms. The warm and moist air rises due to the Chotanagpur Plateau, Himalayan ranges, and Assam Plateau. Thunder and lightning is common with a nor'wester. Nor'westers are more frequent in the late afternoon because of the influence of surface heating in producing convection currents in the atmosphere. In the western region of Bangladesh, nor'westers come in the late afternoon and before evening but in the eastern side it comes generally after evening, moving from a northwesterly to a easterly and southeasterly direction. In this season the morning remains calm. Temperature begins to rise from noon creating a convective current and the storm is formed. The average wind speed of a nor'wester is 40-60 km per hour. But in exceptional circumstances the wind speed may exceed 100 km. The duration of the storm is generally less than an hour but sometimes it may exceed an hour.

Much of the country’s rural population lives in huts made of corrugated iron or mud and straw which are ill-equipped to withstand winds powerful enough to uproot trees and knock down electricity pylons.

Norwesters may also strike later in November. Given their ferocity and destructive capacity `norwesters’ are also referred to as tornadoes. For nearly 60 days during the two storm seasons, locally generated storms have hit various parts of the country almost on a daily basis. So far there is no effective early warning system for these storms. They are so local in nature and take shape so suddenly that modern tracking devices can only locate them when they begin to move, at times with a whirling speed of 200 km.

In Dhaka, trees were uprooted and thatched roofs blown away after a powerful storm struck the capital on 2 May 2008. The storms are so frequent in number and so destructive in nature that the total damage done by them is perhaps only second to the damage caused by the annual floods. In terms of damage to life and property, they do more than the floods.

Norwesters often strike when the country’s ‘boro’ crop - the country’s main rice harvest - is ready for harvest, and jute, a major cash crop for the impoverished nation, is at a critical stage of growth. According to the department of meteorology, 30-50 percent of standing crops are damaged in areas where ‘norwesters’ hit.

The crop loss could be minimised or even avoided if the pattern of cultivation is changed, either by planting the crops two to three weeks earlier than now, or by shortening the harvesting season. Most of those who die, die indoors, crushed under mud walls or hit by flying tin roofs - the construction of disaster-resilient houses could save thousands of lives lost under falling roofs and walls.

http://www.irinnews.org/report.aspx?ReportId=78089
http://banglapedia.search.com.bd/HT/N_0208.htm

The tropical cyclone Nargis in the Bay of Bengal is on course towards the west coast of Myanmar. It is expected to hit the lowest central part of the country, the Ayeyarwady (or Irrawaddy) delta near the great city of Yangon (also known as Rangoon) and the low coast to the north of it. In the northern hemisphere a cyclone rotates counter-clockwise, because of the coriolis force, which means that water masses from the Bay of Bengal will be forced far over land on the right side of the cyclone, where the delta is. Further north the mountain range Arakan Yoma (also known as the Chin Hills) forms a wall towards the bay, and here Nargis is expected to release torrential rains, when the humid air is forced up over the up to 3000 m high mountain tops.

The majority of Burma's Myanmar's population lives in the Ayeyarwady valley. The upper and central portions of the Ayeyarwady delta are almost entirely under cultivation, principally for rice. The climate is monsoonal climate, with an average annual rainfall of about 1,500-2,000 mm in the north increasing to 2,500 mm in the southeast and 3,500 mm in the southwest. Over 90% of the rain falls between mid May and mid November.

Sorry at my age we sometimes have difficulties with "new" geographical names, but I do my utmost to keep to the official, politically correct, spelling.

• http://www.gdacs.org/reports.asp?eventType=TC&ID=NARGIS-08&system=asgard&alertlevel=Green&glide_no=&location=&country=&new=true
• http://www.arcbc.org.ph/wetlands/myanmar/mmr_irrdel.htm



PS of 30 April 2008
Bangladesh raises storm alert and urges swift rice harvest: http://www.alertnet.org/thenews/newsdesk/DHA224084.htm
The cyclone can also be tracked here, with up to 72 hours lead: http://tsr.mssl.ucl.ac.uk/

PS of 3 May 2008: See follow up here.

The greatest earthquakes occur in subduction zones, where one tectonic plate is sliding beneath another. Virtually all of the big earthquakes, the ones of magnitude eight or nine or above, happen at sea. The largest earthquake ever recorded is no exception to this rule.

The epicentre of the Great Chilean Earthquake of 22 May 1960 was about 160 km off the coast of Chile in the Peru-Chile Trench (39.5° S, 74.5° W) with a focal depth of 33 km. Two days later, on 24 May 1960, Cordón Caulle, a fissure vents system located in the Chilean Lake District, erupted, sending ash and steam as high as 6 km.

At the Peru-Chile trench the Nazca Plate is subducted beneath the South American Plate. In the area hit by the earthquake the dip of the subduction zone is about 30° and the subduction gives rise to an arc of still active volcanoes.

Buildings fell all along the Chilean coast from Conception to the southern end of Isla Chilor. The towns of Valdivia and Puerto Montt were devastated. (The earthquake is also known as the 1960 Valdivia earthquake / Gran terremoto de Valdivia).

The earthquake set off huge landslides and sent rocks and boulders tumbling down the mountain sides. The land around the city of Puerto Montt sank and coastal areas were flooded. Rivers had their courses changed and landslides created new lakes. Many of the landslides occurred in the Chilean Lake District from Lago Villarica to Lago Todos los Santos.

The earthquake set off huge tsunamis which radiated out from the epicentre, travelling at speed of up to 350 km/h, the Chilean coast was devastated by a 25 (or was it 12 ?) m high tsunami which arrived 10 to 15 minutes after the quake. Remains of houses were carried inland as much as 3 km. There was also severe damage in the Philippines, Hawaii and the japan.

Over 2000 people died and 3000 were injured. 2 million people became homeless. There were not extremely large numbers of victims, for such an earthquake, because the population was alerted on that something was going to happen by previous shakes and underground noise.

Map of some of the places mentioned and the most important volcanoes in the district. In 2005 we made our way from Puerto Montt to San Carlos de Barriloche in Argentina through the Chilean Lake District (bus, boat, bus, boat, bus) - as many tourists do. Under way I photographed the following volcanoes: Osorno (famous for its Fujiyama look), Puntiagudo ("Volcán Puntiagudo" (Spanish for "Sharp-pointed Volcano") is a stratovolcano with a prominent 2,493 m high sharp-pointed summit that results from glacial dissection and gets its name from this feature), and Tronador. See the 3 photos below.

• http://earthquake.usgs.gov/regional/world/events/1960_05_22.php
• http://en.wikipedia.org/wiki/Great_Chilean_Earthquake
• http://www.gochile.cl/html/ChileValdivia/Chile-Valdivia-Terremoto.asp
• http://www.geophys.washington.edu/tsunami/general/historic/chilean60.html
• http://www.usgs.gov/faq/list_faq_by_category/get_answer.asp?id=154





Notes:
The volcano Puyehue is often cited as the volcano that erupted on 24 May, but actually it was the nearby fissure volcano Cordón Caulle. Although Cordón Caulle is sometimes listed as part of Puyehue volcano, it is tectonically and magmatically distinct from Puyehue. No historical eruptions are known from Puyehue, and eruptions in 1921-22 and 1960 listed in some sources actually occurred at Cordón Caulle volcano located to the Northwest.

As far as I know the epicentre of the main quake was at 39.5° S, 74.5° W - some maps however show it inland (including the USGS map). Well of course there were more than one shock, but even then?

Can earthquakes trigger volcanic eruptions? The volcanic eruption 2 days after the 1960 Chilean earthquake has been taken as evidence, but that could still be a coincidence, and the question is still debated. That volcanoes, on the other hand, can cause earthquakes, is well known.

What I wanted to stress here is the role of subduction zones for important natural hazards like earthquakes, volcanoes, tsunamis and landslides.