Fact File; Popocatapetl

Well... it's at it again... so... seeing as I haven't done a fact file on this volcano yet... and now the fact is that it is erupting again makes me think that its about time that I do one.. so... back to my favorite topics... Volcanoes! :)

Fact File; Popocatepetl

 Location;   Popocatepetl is 70 km (43 mi) southeast of Mexico City,
Magma Type- Predominantly Andesitic, but it has also erupted large volumes of Dacite.                                                     Magma produced in the current cycle of activity tends to be a mixture of the two.
Typical eruption style: Dominantly explosive, construction of lava domes. Plinian eruptions at intervals of several centuries or few thousands of years, vulcanian and strombolian activity in intermittent phases.

General Background;  Popocatépetl, whose name is the Aztec word for smoking mountain, towers to 5426 m 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 250-450 m deep crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano.
At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas south of the volcano. The modern volcano was constructed to the south of the late-Pleistocene to Holocene El Fraile cone. Three major plinian eruptions, the most recent of which took place about 800 AD, have occurred from Popocatépetl since the mid Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since pre-Columbian time.

This 2003 photo from the International Space Station shows a pair of volcanoes in Mexico. As part of the “Ring of Fire” stretching around the Pacific, Mexico hosts several of the world’s most continually active volcanoes, including the massive Popocatepetl (Aztec for "Smoking Mountain") at left. The neighbouring volcano is Iztaccíhuatl (the "Woman in White"). The faint plume emanating from Popocatepetl’s summit crater shows the ever-present hazard the volcano represents to the 25 million people living in the region, including the nearby city of Amecameca, as well as the metropolitan centres of Mexico City to the northwest and Puebla to the east. Credit: NASA

Danxia Landform!!! Amazing :)

The Danxia landform refers to various landscapes found in southeast and southwest China that "consist of a red bed characterized by steep cliffs". It is a unique type of petrographic geomorphology found in China. Danxia landform is formed from red-coloured sandstones and conglomerates of largely Cretaceous age. The landforms look very much like karst topography that forms in areas underlain by limestones, but since the rocks that form danxia are sandstones and conglomerates, they have been called "pseudo-karst" landforms. Danxia landforms cover several provinces in southeast China. 

Taining County, Fujian Province, has very good examples of "young" danxia landforms wherein deep, narrow valleys have been formed. As the landform gets older, valleys widen and one gets isolated towers and ridges.

The danxia landform is named after Mount Danxia, one of the most famous examples of the danxia landform.

A very peculiar feature of danxia landscape is the development of numerous caves of various sizes and shapes. The caves tend to be shallow and isolated, unlike true karst terrain where caves tend to form deep, interconnecting networks.

In 2010, several danxia landscapes in southern China, with a general name of "China Danxia", were inscribed as a World Heritage Site.

The six inscribed danxia landform areas are: Mount Langshan and Mount Wanfoshan (Hunan Province), Mount Danxia (Guangdong Province), Taining and Guanzhishan (Fujian Province), Mount Longhu and Guifeng (Jiangxi Province), Fangyan, Mount Jianglang (Zhejiang Province), and Mount Chishui (Guizhou Province). The total core area of 6 regions above is 73945 ha, and the total buffer area is 65446 ha.

So... just a quick something that caught my eye.

The Medditeranian Sea

Well... sorry for the long wait! having just completed a temporary move to the south of france... The Alpes Maritimes to be exact... this has given me a new focus for the time being.. the geological history of the south of France, The Alps in all their current snowy glory and the Mediterranean sea in general... including interesting things like Cyprus, Morocco, Greece, Turkey, Italy and its volcanoes, Santorini... anyhow... you get the picture!
To start with .... 


A broad Overview of the Mediterranean sea.

The Mediterranean Sea.

The Mediterranean Sea is a connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Europe and Anatolia, on the south by North Africa, and on the east by the Levant.

The sea is sometimes considered a part of the Atlantic Ocean, although it is usually identified as a completely separate body of water.

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,267 m (17,280 ft) in the Calypso Deep in the Ionian Sea.

It was an important route for merchants and travellers of ancient times that allowed for trade and cultural exchange between emergent peoples of the region. The history of the Mediterranean region is crucial to understanding the origins and development of many modern societies. "For the three quarters of the globe, the Mediterranean Sea is similarly the uniting element and the centre of World History."

The Mediterranean Sea is connected to the Atlantic Ocean by the Strait of Gibraltar in the west and to the Sea of Marmara and the Black Sea, by the Dardanelles and the Bosporus respectively, in the east. The Sea of Marmara is often considered a part of the Mediterranean Sea, whereas the Black Sea is generally not. The 163 km (101 mi) long man-made Suez Canal in the southeast connects the Mediterranean Sea to the Red Sea.

The International Hydrographic Organization defines the limits of the Mediterranean Sea as follows:

Stretching from the Strait of Gibraltar in the West to the entrances to the Dardanelles and the Suez Canal in the East, the Mediterranean Sea is bounded by the coasts of Europe, Africa and Asia, and is divided into two deep basins:

• Western Basin:
• On the west: A line joining the extremities of Cape Trafalgar (Spain) and Cape Spartel (Africa).
• On the northeast: The West Coast of Italy. In the Strait of Messina a line joining the North extreme of Cape Paci (15°42'E) with Cape Peloro, the East extreme of the Island of Sicily. The North Coast of Sicily.
• On the east: A line joining Cape Lilibeo the Western point of Sicily (37°47′N 12°22′E), through the Adventure Bank to Cape Bon (Tunisia).
• Eastern Basin:
• On the west: The North-eastern and Eastern limits of the Western Basin.
• On the northeast: A line joining Kum Kale (26°11'E) and Cape Helles, the Western entrance to the Dardanelles.
• On the southeast: The entrance to the Suez Canal.
• On the east: The coasts of Syria and Palestine.

(It should be noted that the coast referred to as belonging to Palestine in this document dating to 1953 has been within the internationally recognised borders of the country known as Israel since 1948. Of the territories administered by the Palestinian Authority, only the Gaza Strip has a sea coast.)

Being nearly landlocked affects conditions in the Mediterranean Sea: for instance, tides are very limited as a result of the narrow connection with the Atlantic Ocean. The Mediterranean is characterized and immediately recognised by its deep blue colour.

Evaporation greatly exceeds precipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin. Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to increase eastward. This pressure gradient pushes relatively cool, low-salinity water from the Atlantic across the basin; it warms and becomes saltier as it travels east, then sinks in the region of the Levant and circulates westward, to spill over the Strait of Gibraltar. Thus, seawater flow is eastward in the Strait's surface waters, and westward below; once in the Atlantic, this chemically distinct Mediterranean Intermediate Water can persist thousands of kilometres away from its source.

The geologic history of the Mediterranean is complex. It was involved in the tectonic break-up and then collision of the African and Eurasian plates. The Messinian Salinity Crisis occurred in the late Miocene (12 million years ago to 5 million years ago) when the Mediterranean dried up. Geologically the Mediterranean is underlain by oceanic crust.

The Mediterranean Sea has an average depth of 1,500 m (4,900 ft) and the deepest recorded point is 5,267 m (17,280 ft) in the Calypso Deep in the Ionian Sea. The coastline extends for 46,000 km (29,000 mi). A shallow submarine ridge (the Strait of Sicily) between the island of Sicily and the coast of Tunisia divides the sea in two main sub regions (which in turn are divided into subdivisions), the Western Mediterranean and the Eastern Mediterranean. The Western Mediterranean covers an area of about 0.85 million km² (0.33 million mi²) and the Eastern Mediterranean about 1.65 million km² (0.64 million mi²). A characteristic of the Mediterranean Sea are submarine karst springs or vruljas, which mainly occur in shallow waters and may also be thermal.

Tectonic evolution

The geodynamic evolution of the Mediterranean Sea was provided by the convergence of European and African plates and several smaller microplates. This process was driven by the differential seafloor spreading along the Mid-Atlantic Ridge, which led to the closure of the Tethys Ocean and eventually to the Alpine orogenesis. However, the Mediterranean also hosts wide extensional basins and migrating tectonic arcs, in response to its land-locked configuration.

According to a report published by Nature in 2009, scientists think that the Mediterranean Sea was mostly filled during a time period of less than two years, in a major flood (the Zanclean flood) that happened approximately 5.33 million years ago, in which water poured in from the Atlantic Ocean and through the Strait of Gibraltar, at a rate three times the current flow of the Amazon River

Eastern Mediterranean

In middle Miocene times, the collision between the Arabian microplate and Eurasia led to the separation between the Tethys and the Indian oceans. This process resulted in profound changes in the oceanic circulation patterns, which shifted global climates towards colder conditions. The Hellenic arc, which has a land-locked configuration, underwent a widespread extension for the last 20 Ma due to a slab roll-back process. In addition, the Hellenic Arc experienced a rapid rotation phase during the Pleistocene, with a counter clockwise component in its eastern portion and a clockwise trend in the western segment.

Central Mediterranean

The opening of small oceanic basins of the central Mediterranean follows a trench migration and back-arc opening process that occurred during the last 30 Myr. This phase was characterised by the anticlockwise rotation of the Corsica-Sardinia block, which lasted until the Langhian (ca.16 Ma), and was in turn followed by a slab detachment along the northern African margin. Subsequently, a shift of this active extensional deformation led to the opening of the Tyrrenian basin.

Western Mediterranean

The Betic-Rif mountain belts developed during Mesozoic and Cenozoic times, as Africa and Iberia converged. Tectonic models for its evolution include: rapid motion of Alboran Domain, subduction zone and radial extensional collapse caused by convective removal of lithospheric mantle. The development of these intramontane Betic and Rif basins led to the onset of two marine gateways which were progressively closed during the late Miocene by an interplay of tectonic and glacio-eustatic processes.

Pale environmental analysis

Its semi-enclosed configuration makes the oceanic gateways critical in controlling circulation and environmental evolution in the Mediterranean Sea. Water circulation patterns are driven by a number of interactive factors, such as climate and bathymetry, which can lead to precipitation of evaporates. During late Miocene times, a so-called "Messinian Salinity Crisis" (MSC hereafter) occurred, which was triggered by the closure of the Atlantic gateway. Evaporates accumulated in the Red Sea Basin (late Miocene), in the Carpatian foredeep (middle Miocene) and in the whole Mediterranean area (Messinian). An accurate age estimate of the MSC—5.96 Ma—has recently been astronomically achieved; furthermore, this event seems to have occurred synchronously. The beginning of the MSC is supposed to have been of tectonic origin; however, an astronomical control (eccentricity) might also have been involved. In the Mediterranean basin, diatomites are regularly found underneath the evaporate deposits, thus suggesting (albeit not clearly so far) a connection between their geneses.

The present-day Atlantic gateway, i.e. the Strait of Gibraltar, finds its origin in the early Pliocene. However, two other connections between the Atlantic Ocean and the Mediterranean Sea existed in the past: the Betic Corridor (southern Spain) and the Rifian Corridor (northern Morocco). The former closed during Tortonian times, thus providing a "Tortonian Salinity Crisis" well before the MSC; the latter closed about 6 Ma, allowing exchanges in the mammal fauna between Africa and Europe. Nowadays, evaporation is more relevant than the water yield supplied by riverine water and precipitation, so that salinity in the Mediterranean is higher than in the Atlantic. These conditions result in the outflow of warm saline Mediterranean deep water across Gibraltar, which is in turn counterbalanced by an inflow of a less saline surface current of cold oceanic water.

The Mediterranean was once thought to be the remnant of the Tethys Ocean. It is now known to be a structurally younger ocean basin known as Neotethys. The Neotethys formed during the Late Triassic and Early Jurassic rifting of the African and Eurasian plates.

Paleoclimate

Because of its latitudinal position and its land-locked configuration, the Mediterranean is especially sensitive to astronomically induced climatic variations, which are well documented in its sedimentary record. Since the Mediterranean is involved in the deposition of eolian dust from the Sahara during dry periods, whereas riverine detrital input prevails during wet ones, the Mediterranean marine sapropel-bearing sequences provide high-resolution climatic information. These data have been employed in reconstructing astronomically calibrated time scales for the last 9 Ma of the Earth's history, helping to constrain the time of past Geomagnetic Reversals.

 Furthermore, the exceptional accuracy of these paleo-climatic records have improved our knowledge of the Earth's orbital variations in the past.

So there you have it... A broad overview of the Mediterranean sea. It is a truly magical place... good times were had by all!