lunes, 31 de octubre de 2016

Monthly Geological Pics



El sólo mérito de su altura, hacen del Aconcagua una singularidad geológica digna de figurar en esta sección…. y es que se trata de la montaña más alta de América… 

No sé si esto es decir mucho o poco, porque ni siquiera alcanza los 7.000 metros y, aunque he conocido gente absolutamente normal que se ha pagado un viaje de agencia hasta la cumbre, no es menos cierto que la montaña a veces da sus zarpazos, y se lleva por delante la vida quizás no de montañeros o alpinistas, pero sí de aventureros. Para eso, no hacen falta de hecho montañas tan altas.

The only merit of its height, makes the Aconcagua a worthy geological uniqueness to include in this section .... and yet it is the highest mountain in America ... I do not know if this is a much to say or not, since it does not even reaches 7,000 meters and, although I have known quite normal people who paid a travel agency to take them to the summit, the fact remains that the mountain sometimes shows its claws, and takes its life tributes… 

Geologically the Aconcagua region is a key area to analyze the geological evolution of the Main Andes, which constitutes its peak area. Its high elevation does not correspond to an active volcano, but is the result of tectonic uplift of the range, controlled by the subduction occurring off the Pacific coast of Chile ... 

Geológicamente la región del Aconcagua constituye un área clave para analizar la evolución geológica de la cordillera Principal de los Andes, de la que constituye su punto culminante. Su gran elevación no corresponde a un edificio volcánico activo, sino que es el resultado del levantamiento tectónico de la cordillera, controlado por la subducción que se produce frente a la costa pacífica de Chile… y en la que interactúan las placas de Nazca y Sudamérica.

En vuelo a Santiago, no es difícil ver el Aconcagua por la ventanilla. Es inconfundible. Una mole de roca andesítica, oscura, parcheada de manchas blancas de la nieve aferrada a su cumbre y a sus laderas. Laderas escarpadas y desnudas, descarnadas y recubiertas también de pedreras.

The geological description of the Aconcagua region has followed, since the nineteenth century, a swing of controversial explanations of its origin. The first field observations described the top of the hill like sandstone, limestone and gypsum, whose layered nature could not correspond with a volcano. However both volcanic Mount Aconcagua and La Ramada rocks were wrongly assigned to a current volcanic edifice when they are actually allochthonous deposits.

On January 20, 1835, a British merchant observed from the port of Valparaiso an erupting volcano and assumed that it was the Aconcagua. Just at that time Charles Darwin was walking through the port, to whom he told the story. Darwin had observed an eruption of Osorno volcano from the boat when they were heading north to Valparaiso. On that basis, the scientist repeated on several occasions, circles and publications that Aconcagua was an active volcano. His fame and prestige avoided questioning the claim until much later.

German Walter Schiller can be considered the greatest architect of knowledge of the geology of Aconcagua and although his greatest contributions date back to the early twentieth century, his Tectonic revolutionary ideas would not be fully accepted until past half century. His masterful work published in 1912: "The High Cordillera of San Juan and Mendoza and part of the province of San Juan," was misinterpreted and his conclusions were rejected. His remarks were reinterpreted, tectonic repetitions where simplified and even the great thrusts that he described were questioned. Only in the 70s, the detailed study of the main ridge in the San Juan sector made return to Schiller's ideas regarding structures and landslides in the Andes at these latitudes.

El basamento de los Andes en la zona del Aconcagua presenta una historia compleja de acreciones y colisiones entre diferentes terrenos. Los afloramientos de depósitos y rocas comienzan con un basamento previo al Jurásico. En el Mioceno, hace 20Ma, se emplaza un arco magmático que da origen al Complejo Volcánico Aconcagua, nombre con que se conoce a las rocas volcánicas de este cerro. Los materiales eruptivos de una serie de volcanes se depositan discordantes con las rocas de la cobertera sedimentaria jurásica y cretácica previamente deformada. Posteriormente estos edificios volcánicos son erosionados hasta no quedar pista de ellos. Por último, hace unos 8Ma se produce el evento final de la Cordillera Principal en estas latitudes, plegando y elevando las rocas yacentes, y dando lugar al levan tamiento del cerro Aconcagua hasta las alturas que conocemos hoy en día.

The basement of the Andes in the Aconcagua area has a complex history of collisions and accretions occurred between different terrains. Deposits and rocks outcrops begin with a pre-Jurassic basement. In the Miocene, 20Ma ago, a magmatic arc stablishes that gives rise to the Aconcagua Volcanic Complex, name by which are known the volcanic rocks of this mountain. Eruptive materials of a series of volcanoes are deposited in discordance with the previously deformed rocks of the Jurassic and Cretaceous sedimentary cover. Subsequently all these volcanic edifices are eroded so that no track of them remains today. Finally, approximately 8MA ago, the final event of the Principal Cordillera in those latitudes occurs, folding and raising the rocks. During this movement it is that the Aconcagua is lifted to the heights we know today.

Para más detalles…: 

jueves, 20 de octubre de 2016

The landscape collector



Mediado octubre y al cabo de uno de los veranos más duros que recuerdo…, ¡prueba superada!, por fin llegan las lluvias otoñales para aliviar tanta canícula, tanta sequía… tanta desazón de ver el paisaje yermo, seco y estéril.

El río manchego que en la primavera era un cauce de vida y el escenario de una naturaleza lujuriosa, se convirtió, con el paso del largo verano: julio, agosto y septiembre en un lecho seco de guijarros ardientes… “cauce gris en entorno amarillo” diría un título a lo Miró.

En sus pozas, hace ya tres meses, entre mayo y julio y con el contrapunto aflautado de la oropéndola, pescaba la siempre recatada, la siempre preciada y la siempre escasa cigüeña negra a la que no lejos, esperaban sus cuatro exigentes pollos, opuestamente blancos, ávidos de peces… y a la caída de la tarde, acudían discretamente las ciervas con sus pequeños, a beber el agua fresca y vivificante, mientras el autillo cantaba en la frondosa ribera.

Más tarde, a partir del mes de agosto , solo los jabalíes aprovechaban aún los charcos que de día en día eran más exiguos, apenas alimentados por un hilo de agua, luego por un goteo y finalmente, expuestos a una acelerada e inexorable evaporación que ni siquiera aliviaba una  tormenta de temporada…

Finalmente los charcos se hicieron barro reseco, y el cauce dejó emerger los cantos del lecho.

Como en la cámara rápida de un documental, las primeras lluvias otoñales le han devuelto al río un mínimo de su esencia y dignidad… un flujo de agua que nos dice que el ciclo vuelve a empezar, aún con el contrapunto de los fresnos y los quejigos que, apenas empezando a amarillear también nos dicen que el ciclo del agua y el de los árboles están descompasados…: las hojas aún habrán de caer y los árboles aún habrán de pasar el crudo invierno para también renacer...

martes, 11 de octubre de 2016

Arma letal / Letal weapon

The young goshawk has caught a rabbit ... a whole adult rabbit. It can feel proud, and so betrays his gaze. It is not the first rabbit he hunts, but in its almost two years of life, most of his prey have been birds, many kinds of them...: magpies, jays, doves; also lizards, rarely a small rodent, and sometimes, even some carrion. However, the rabbit, the staple food of carnivorous predators of spanish nature, is not one of his main prey.

But a rabbit, healthy, adult and jovial ... is not only a source of pride, it is also a guarantee of a good meal, a tasty and juicy food, and puts the young goshawk live up to the great eagles, which sail fly over the mountains, the plains and the meadows, and whenever they see a rabbit, they infallibly go for him.

It’s true that the rabbit was clueless and unaware, and cluelessness cost him his life; It was surprised when the goshawk passed over a clearing in the dwelling forest; he had not thought of catching him, nor stalked ... but the goshawk is very fast, very agile, he does not miss anything ... and "catches on the fly".

The goshawk…, a medium-sized bird of prey inhabiting the forests. It flies with agility and a prodigious speed and ability to maneuver between the trees, alternating small glides and fast wing shakes, acrobatics, turns, braking, twists and leg support to the trunks, which allows him to catch small prey inside the forests.

Rabbits are not forest animals, nor usually are they found in much of the range of goshawk. Sometimes however, the predator, especially young and immature, fly over the open or forest clearings, and do not waste a chance encounter.

The hawk is a species that is distributed widely but unevenly, throughout the forests of mainland Spain.

This is actually one of the fiercest and boldest birds. The young goshawk does not know well what to do. He is excited ... It does not always kill such a large animal and his blood boils. He should hide his prey as soon as possible, take it to a perch where to enjoy it quietly, discreetly, hidden from other opportunistic animals. But is it  not too heavy to fly with it?

domingo, 9 de octubre de 2016

El abejaruco / The bee-eater

En pleno mes de octubre, me llegan los recuerdos de la primavera, recapitulamos... 
Mayo..., la colonia de abejarucos se encontraba en plena actividad… febril actividad… consiguiendo insectos para alimentarse y para alimentar a sus parejas que incuban en la oscuridad de los nidos subterráneos… 

Agua de mayo, que esperan los aficionados a los pájaros, … Aves multicolores, alegres, gregarias y viajeras… 

“Andaba por el campo y de pronto, una llamada leve me hizo volver la cabeza al cielo. Insistió el silbido. Arriba, velocísimo, parado, fino, entre verde y amarillo, las alas y el pico agudos,… los abejarucos”.

Podría decirse que el abejaruco es el ave más bonita de cuantas habitan en España…? 

Para mí sí… parte de un plantel en el que incluyo a la Carraca, al Martín pescador y a la Oropéndola. 

Azules verdosos en la zona ventral, con una franja negra que separa la garganta que es de color amarillo; Por la parte superior, el color predominante es el castaño; En la cara destaca la frente blanca separada por un antifaz negro que llega hasta los oídos y que es como si fuera una prolongación del pico incurvado y de la misma tonalidad negra; Los ojos de un rojo vivo quedan enmarcados dentro de ese antifaz; Las alas de forma puntiaguda también son de color azul verdoso y en su zona media son de color castaño; La cola es verde parduzca, siendo las plumas centrales más sobresalientes. 

Aves alegres…, que pasan el día realizando cortos vuelos acrobáticos, persiguiendo insectos en escuadrillas, mientras silban en el aire… comunicándose unos con otros, quien sabe si sincronizando su estrategia de combate aéreo…

Aves gregarias… que tan pronto se encuentran posadas en grupo en los cables del tendido eléctrico…, en una alambrada…, o emprenden juntas el vuelo para ir a perseguir a sus presas con sus giros cerrados, sus picados y sus vuelos rasantes…
 … y viajeras… En la primavera aprovechamos para observar aquellas aves que nos visitan desde tierras lejanas… Abubillas, Águilas calzadas y culebreras, Primillas, Cenizos, Cigüeñas negras, Golondrinas, Carracas y por supuesto Abejarucos… todas preferidas, todas predilectas…
Con el abejaruco se da una curiosa paradoja… y es como una especie tan bonita y llamativa es cada vez más abundante… y está aumentando su territorio poco a poco más al norte, quizás condicionada por el tan comentado calentamiento global de la tierra... a veces aprovechando los taludes que genera el propio ser humano... 

 … y viajeras, decía… 
En pleno mes de octubre, los abejarucos emprenden su viaje de regreso al sur..., buen viaje.

martes, 4 de octubre de 2016

Geology behind the Sphinx

In geological Eocene times, some 50 million years ago, most of present-day Egypt was submerged under the sea. Sedimentation and decomposing remains of marine organisms formed a carbonated mud. As the sea receded, mud petrified into a consolidated and hardened sedimentary rock, forming banks of limestone from which the pyramid builders quarried limestone blocks and from which they carved the Sphinx.
Natural limestone of the Giza Plateau in which lowest layers the Sphinx is carved is known as the Mokkatam Formation. Sphinx geological layers have been labeled as Member I, Member II, and Member III.
The Figure displays a simplified cross-section of the Giza Pyramids Plateau. The Giza Plateau is an outcrop of the Middle Eocene Mokkatam Formation. A second outcrop of the Upper Eocene Maadi Formation borders the Pyramids Plateau. A large sandy wadi separates the Mokkatam Formation from the Maadi Formation.
The Sphinx within the Giza geology

The lowest stratum of the statue, Member I, is the hard and brittle rock of an ancient reef limestone containing nummulite fossils easy to identify. This layer rises to a height of four meters at the Sphinx’s rump and only one meter at the paws.
Most of the Sphinx body is cut into Member II, seven layers that alternate softer and harder limestone, marls and claystone, as they rise in elevation. This layers show large flakes of marly limestone blow off the walls of the Sphinx quarry and since ancient times until recent restorations, most of the Sphinx body was protected by masonry cover.
Member III, from which the neck and head are carved, is softer at the neck and harder at the head. This is a good building stone. Member III’s durability explains the remarkable preservation of the Sphinx’s face while the statue’s body has been ravaged by weathering.

What happended to the nose…?

Legends have passed over hundreds of years regarding this question: What happened with the Sphinx’s nose?

Many of us have heard the tale that a cannonball fired by Napoleon’s soldiers hit the nose and caused it to break off. This is not true, since sketches of the Sphinx published well before the era of Napoleon  illustrate it without a nose…

The Egyptian Arab historian al-Magrizi wrote in the 15th century that the nose was actually destroyed by a Sufi Muslim named Muhammad Sa'im al-Dahr. In 1378 Egyptian peasants made offerings to the Great Sphinx in the hope of controlling the flood cycle, which would result in a successful harvest. Outraged by this blatant show of devotion, Sa'im al-Dahr destroyed the nose and was later executed for vandalism. Whether this is absolute fact is still debatable.

Long-term deterioration

With the Sphinx rapid erosion, age has been set to be not older than 4,500 years, tied to Pharaoh Khafre’s building program at Giza.

Until recent years, the Sphinx was still disintegrating. In the 1980s, two sizeable stones fell from the statue: masonry veneer from the left hind paw in 1981 and a large piece of bedrock from the right shoulder in 1988. The Supreme Council of Antiquities’ decade-long restoration in the 1990s was only the latest of the repairs to the Sphinx that began at least in the New Kingdom (1550-1070 BC).

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