Friday, March 30, 2012 8:24:07 AM
About a week ago explorer-filmmaker James Cameron dived into the Mariana Trench. Very appropriately NASA Earth Observatory a few days later published an image of one of the Northern Marianas islands.
At the Mariana trench the Pacific plate is subducted beneath the Mariana Plate, creating the deepest subduction trench on Earth (deepest point being the Challenger deep with a depth of 10,900 m), and further to the west the arc of the Mariana islands.
On the cross section above the Alamagan Island is shown as an example of one of the Mariana islands. It might as well have been the Pagan Island a bit further north.
In this photograph a steam plume flows blows south from the peak of Pagan Island’s northernmost volcano. Pagan is part of the Commonwealth of the Northern Marianas, an island chain of volcanoes that form the margin between the Pacific Ocean (to the east) and the Philippine Sea (to the west). Pagan is made up of two stratovolcanoes separated by an isthmus, and it is one of the more volcanically active islands in the Marianas. The island was completely evacuated in 1981 when a large eruption forced the small Micronesian community to flee. Before the early months of 2012, the most recent eruption occurred in 2010. The islands themselves mark the tectonic boundary where the old, cold Pacific plate is being subducted at the Marianas trench beneath the younger, less dense crust of the Philippine Sea. The subduction results in substantial volcanic activity on the upper plate, forming the island arc of the Marianas. The Marianas Trench is onsidered to be one of the classic examples of an oceanic subduction zone.
Geology, plate tectonics, volcanoes, trench
Tuesday, March 27, 2012 9:37:43 AM
NOAA (US National Oceanic and Atmospheric Administration) has registered a 10.8 cm x 5 cm x 5.7 cm hailstone which hit Hawaii (Oahu Island) on 9 March 2012
Hail the size of golf balls and baseballs can only form within intense thunderstorms called supercells. These supercells need warm, moist air to rise into progressively colder, drier air, as well as winds changing direction and increasing speed with increasing height off the ground. For both sets of conditions to exist at the same time in Hawaii is extremely rare, but that did occur on 9 March. Conditions that day were ideal for a supercell to form — which on National Weather Service radar imagery looked very much like that from such storms in the central portions of the contiguous United States where severe hail larger than 2.5 in diameter is most common.
Supercells can also produce tornadoes, another rarity in Hawaii.
Monday, March 19, 2012 9:32:42 AM
The new state South Sudan has been in the news lately for several reasons a.o.:
Tuesday 13 March Sudan and South Sudan initiated two agreements on status of nationals and demarcation of common boundary in the context of a spirit of cooperation and partnership http://www.mmegi.bw/index.php?sid=11&aid=429&dir=2012/March/Thursday15
South Sudan 'has 2,000 child soldiers' http://news.yahoo.com/south-sudan-2-000-child-soldiers-un-155815973.html
The number of people killed in South Sudan in the latest of a series of cattle raids has risen to more than 200 http://www.bbc.co.uk/news/world-africa-17338139
A United Nations special envoy on Thursday 15 March warned of the possibility of “large scale humanitarian crisis” in the word’s newest nation, unless resources are mobilized to ensure protection and safety of children returning from neighboring north. http://www.sudantribune.com/UN-warns-of-humanitarian-crisis-in,41927
And so on and so forth.
Within all this news from a new state trying to find its feet I find it refreshing to see the birth of a new blog - NO NOT on geology - but on BIRDING in South Sudan
written by a Juba resident. A hearty welcome !
Monday, March 5, 2012 8:10:58 AM
Most sand deserts consist of quartz sand, but White Sands has got its name because its main constituent is (white) gypsum. Normally desert sand becomes extremely hot when the sun is shining, but the white gypsum in White Sands reflect most of the sun radiation back into the atmosphere (albedo effect) so that the desert remains relatively cool.
The White Sands in New Mexico is the world’s largest gypsum dune field, stretching over 710 km2
. Gypsum is rarely found in the form of sand because it is water-soluble. Normally, rain would dissolve the gypsum and carry it to the sea. The basin, in which the White sands lie, is enclosed and has no outlet to the sea, so that rain that dissolves gypsum from the surrounding mountains is trapped within the basin. Thus water either sinks into the ground or forms shallow pools which subsequently dry out and leave gypsum in a crystalline form, called selenite, on the surface. During the last ice age, a lake covered much of the basin. When it dried out, it left a large flat area of selenite crystals. Another lake is a dry lake bed, at one of the lowest points of the basin, which occasionally fills with water. Much of the ground is covered with selenite crystals which reach lengths of up to 1 m. Weathering and erosion eventually breaks the crystals into sand-size grains that are carried away by the prevailing winds from the southwest, forming white dunes. Winds occasionally lift the gypsum sands into the air. A gypsum dust storm emerged from the dunes in late February 2012.
The dust blowing out of White Sands National Monument was part of a larger pattern of dust storms in the region, including dust in Mexico, Kansas, and Oklahoma.
is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space. It is a measure of the reflectivity of the earth's surface.