Origin of Australopithecus

The origin of Australopithecus, the genus which is widely regarded as ancestral to Homo, is a central problem in human evolutionary studies. Australopithecus species differ considerably from extant African apes and candidate ancestral hominids such as Ardipithecus, Orrorin and Sahelanthropus.

The earliest described Australopithecus species is Australopithecus anamensis, which would be its origin and the probable chronospecies ancestor of Au. afarensis. Here we describe newly discovered fossils from the Middle Awash study area that extend the known Au. anamensis range into northeastern Ethiopia. The new fossils are from chronometrically controlled stratigraphic sequences and date to about 4.1–4.2 million years ago.

They include diagnostic craniodental remains, the largest hominid canine yet recovered, and the earliest Australopithecus femur. These new fossils are sampled from a woodland context. Temporal and anatomical intermediacy between Ar. ramidus and Au. afarensis suggest a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa, involving either replacement or accelerated phyletic evolution.

Australopithecus Afarensis

Australopithecus afarensis was a type of hominid which belonged to the genus Australopithecus and lived between 3.7 and 2.9 million years ago. Australopithecus afarensis was slenderly built, like the younger Australopithecus africanus. It is thought that A. afarensis was ancestral to both the genus Australopithecus and the genus Homo, which includes the modern human species, Homo sapiens. The most famous fossil is the partial skeleton named Lucy (3.2 million years old) by Donald Johanson and colleagues, after they played the Beatles song Lucy in the Sky with Diamonds over and over in celebration of their find.

Compared to the modern and extinct great apes, A. afarensis has reduced canines and molars, although they are still relatively larger than in modern humans. A. afarensis also has a relatively small brain size (~380–430 cm³). The image of a bipedal hominin with a small brain and primitive face was quite a revelation to the paleoanthropological world at the time. This was due to the earlier belief that an increase in brain size was the first major hominin adaptive shift.

Australopithecus afarensis fossils have only been discovered within northern Africa. Despite Laetoli being the type locality for A. afarensis, the most extensive remains assigned to this species are found in Hadar, Afar Region of Ethiopia, including the above-mentioned "Lucy" partial skeleton and the "First Family" found at the A.L. 333 locality. Other localities bearing A. afarensis remains include Omo, Maka, Fejej and Belohdelie in Ethiopia, and Koobi Fora and Lothagam in Kenya.

Selam (Australopithecus Afarensis)

Selam is the name given to a fossilized skull and other skeletal remains of a 3-year-old Australopithecus afarensis female whose bones were first found in Dikika, Ethiopia in 2000 and recovered over the following years. She is often nicknamed Lucy's baby. The remains of Selam have been dated at 3.3 mya, approximately 120,000 years older than "Lucy" (dated to about 3.18 Ma). The fossils were discovered by Zeresenay Alemseged, and are remarkable for both their age and completeness.

On September 20, 2006, the journal Nature presented the findings of a dig in Dikika, Ethiopia a few miles south (across the Awash River) from Hadar, the place where the fossil remains known as Lucy was found. The recovered skeleton comprises almost the entire skull and torso, and many parts of the limbs. The features of the skeleton suggest adaptation to walking upright (bipedalism) as well as tree-climbing, features that correspond well with the skeletal features of Lucy and other specimens of Australopithecus afarensis from Ethiopia and Tanzania. "Lucy's Baby" has officially been nicknamed "Selam" (meaning "peace").

Australopithecus

Australopithecus was a genus of hominids that evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct 2 million years ago. During this time period various different forms of australopiths existed, including Australopithecus anamensis, A. afarensis, A. sediba, and A. africanus. There is still some debate amongst academics whether certain African hominid species of this time, such as A. robustus and A. boisei constitute members of the same genus; if so, they would be considered to be robust australopiths whilst the others would be considered gracile australopiths. However, if these species do indeed constitute their own genus, then they may be given their own name, the Paranthropus.

It is widely held by archaeologists and palaeontologists that the australopithecus played a significant part in human evolution and it was one of the australopith species that eventually evolved into the Homo genus in Africa around 2 million years ago, which contained within it species like Homo habilis, H. ergaster and eventually the modern human species, H. sapiens sapiens.

The brains of most species of Australopithecus were roughly 35% of the size of that of a modern human brain. Most species of Australopithecus were diminutive and gracile, usually standing between 1.2 to 1.4 m tall (approx. 4 to 4.5 feet). In several variations of Australopithecus there is a considerable degree of sexual dimorphism, in this case males are larger than females. Modern hominids do not appear to display sexual dimorphism to the same degree — particularly, modern humans display a low degree of sexual dimorphism, with males being only 15% larger than females, on average. In Australopithecus, however, males can be up to 50% larger than females. New research suggests that sexual dimorphism may be less pronounced than this, but there is still debate on the subject.

Neanderthal Man

The Neanderthal, or Neandertal, was a species of Homo (Homo sapiens neanderthalensis) who lived in Europe and parts of western Asia from about 250,000 to 29,000 years ago, during the Middle Paleolithic period. The first proto-Neanderthal traits appeared in Europe as early as 600,000–350,000 years ago. Proto-Neanderthal traits are occasionally grouped to another species, Homo heidelbergensis.

In 2010, current genetic evidence suggests interbreeding took place with Homo sapiens sapiens (anatomically modern humans) between roughly 80,000 to 50,000 years ago in the Middle East, resulting in Caucasians and Asians having between 1% and 6% more Neanderthal DNA than indigenous sub-Saharan Africans. Specimens with combined Cro-Magnon and Neanderthal traits have also been found in Spain as recently as 40,000 BC suggesting long term and widespread intermingling of "anachronistic races" throughout history.

Neanderthal cranial capacity is thought to have been as large as that of Homo sapiens, in some cases larger, ranging from 1,500 cm3 to 1,650 cm3 (modern human 1,425-1,450 cm3). In 2008, a group of scientists created a study using three-dimensional computer-assisted reconstructions of Neanderthal infants based on fossils found in Russia and Syria, showing that they had brains as large as modern humans' at birth and larger than modern humans' as adults. On average, the height of Neanderthals was comparable to contemporaneous Homo sapiens. Neanderthal males stood about 165–168 cm (65–66 in), and were heavily built with robust bone structure. They were much stronger than Homo sapiens, having particularly strong arms and hands.

The Neanderthal is named after the Neanderthal valley, which is situated about 12 km (7.5 mi) east of Düsseldorf, Germany. The valley itself was named after the theologian Joachim Neander, who lived nearby in Düsseldorf in the late 17th century. The fossil discovered in the Neandertal in 1856, Neanderthal 1, was known as the "Neanderthal skull" or "Neanderthal cranium" in anthropological literature, and the individual reconstructed on the basis of the skull was occasionally called the "Neanderthal man."

Early Neanderthals lived in the Last Glacial age for a span of about 100,000 years. Because of the damaging effects the glacial period had on the Neanderthal sites, not much is known about the early species. Countries where their remains are known include most of Europe south of the line of glaciation, roughly along the 50th parallel north, including most of Western Europe, including the south coast of Great Britain, Central Europe and the Balkans, some sites in the Ukraine and in western Russia and outside of Europe in the Zagros Mountains and in the Levant.

Neanderthal fossils have to date not been found in Africa, but there have been finds rather close to Africa, both at Gibraltar and in the Levant. At some Levantine sites, Neanderthal remains in fact date after the same sites were vacated by Homo sapiens. Mammal fossils of the same time period show that cold-adapted animals were present alongside these Neanderthals in this region of the Eastern Mediterranean. This implies Neanderthals were better adapted biologically to cold weather than modern Homo sapiens and at times displaced modern Homo sapiens (Cro-Magnon) in parts of the Middle East when the climate got cold enough. Cro-Magnon appears to have been the only human type in the Nile River Valley during these periods, and Neanderthals are not known to have ever lived southwest of modern Israel.

Primeval Britons Were Earliest North Europeans

— A University College London archaeologist is part of a team who have unearthed the earliest evidence of human occupation in Britain. Simon Parfitt was part of a team of archaeologists, palaeontologists and earth scientists from the British Museum, the Natural History Museum, UCL, and Queen Mary, University of London, who unearthed the new evidence at an archaeological dig in East Anglia.

Their findings demonstrate that ancient humans occupied Britain over 800,000 years ago, marking the first known settlement in northern Europe -- far earlier than previously thought. The excavation was funded by the British Museum and the work forms part of the Ancient Human Occupation of Britain project, which is funded by the Leverhulme Trust.

The research, published in this week's issue of the scientific journal Nature, reveals over 70 flint tools and flakes excavated on the foreshore at Happisburgh, Norfolk. Mr Parfitt, who is based at the UCL Institute of Archaeology, said: "This challenges our views that early humans spread only during periods of exceptional warmth. Instead, the new evidence demonstrates that early humans were capable of adapting their behaviour as the world changed around them."

Until recently, humans living during this early period in Europe were thought to be confined to the area south of the Pyrenees and Alps, and the earliest finds in Britain were dated from sites like Boxgrove, Sussex, at about 500,000 years. However, in 2005 evidence from Pakefield, Suffolk, indicated that humans had managed to reach Britain about 700,000 years ago, when for a brief period the climate was comparable with that of the Mediterranean today. The findings from Happisburgh extend this record of human presence in Britain even further back in time.

Tools found at Happisburgh provide the first record of Early Pleistocene human occupation on the edges of the cooler -- or 'boreal' -- northern forests of Eurasia. Living near these forests would have presented a range of new challenges to the people living there. Much of northern Europe was covered with boreal forests, which grew and shrank with the ebb and flow of the ice ages. Edible plants and animals were few and far between, and short winter daylight hours and severe winters exacerbated the already tough living conditions that our predecessors faced.

The evidence from Happisburgh indicates that the site lay on an ancient course of the River Thames. This large tidal river would have had freshwater pools and marshes on its floodplain, together with salt marsh and coast nearby.

Mr Parfitt, co-director of the dig in Happisburgh, added: ''The flood plain would have been dominated by grass, supporting a diverse range of herbivores, such as mammoth, rhino and horse. Predators would have included hyaenas, sabre-toothed cats and of course humans.

"The site is exceptional because of the unprecedented preservation of the original materials, from pollen grains to chunks of wood, and mammoth bones to voles and mice. We've even found remains of beetles and plants, which are missing from other sites. What we have in Happisburgh is a complete buried landscape."

(From Science Daily)

Peking Man

Peking Man (Sinanthropus pekinensis) was a type of Homo erectus. A group of fossil specimens was discovered between 1923 and 1927 during excavations at Zhoukoudian (Chou K'ou-tien) near Peking (now Beijing), China. The finds were then dated from roughly 800,000 years ago, although a new 26Al/10Be dating suggests they may be as much as 680,000-780,000 years old. Between 1929 and 1937, 15 partial craniums, 11 lower jaws, many teeth, some skeletal bones and large numbers of stone tools were discovered in the Lower Cave at Locality 1 of the Peking Man site at Zhoukoudian, near Beijing, in China. Their age is estimated to be between 500,000 and 300,000 years old. The fossil skull discovered at Locus E in 1929 was an adolescent or juvenile with a brain size of 915 cc. The skull II, discovered at Locus D in 1929 but only recognized in 1930, was an adult or adolescent with a brain size of 1030 cc.

Fossil Skulls From Africa and Europe

Two fossil skulls, one from central Africa and the other from the Black Sea republic of Georgia, Europe, have shaken the human family tree to its roots, sending scientists scrambling to see if their favorite theories are among the fallen fruit. Probably so, according to paleontologists, who may have to make major revisions in the human genealogy and rethink some of their ideas about the first migrations out of Africa by human relatives.

Although the skulls have caused confusion and uncertainty, scientists speak in superlatives of their potential for revealing crucial insights in the evidence-disadvantaged field of human evolution. The African skull dates from nearly 7 million years ago, close to the fateful moment when the human and chimpanzee lineages went their separate ways. The 1.75-million-year-old Georgian skull could answer questions about the first human ancestors to leave Africa, and why they ventured forth. Still, it was a shock, something of a one-two punch, for two such momentous discoveries to be reported independently in a single week, as happened in July.

Every decade or two, a fossil discovery upsets conventional wisdom. One more possible "missing link" emerges. An even older member of the hominid group, those human ancestors and their close relatives (but not apes), comes to light. Some fossils also show up with attributes so puzzling that scientists cannot decide where they belong, if at all, in the human lineage. At each turn, the family tree, once drawn straight as a ponderosa pine, has had to be reconfigured with more branches leading here and there and, in some cases, apparently nowhere.

The skull of Africa was uncovered in the desert of Chad by a French-led team under the direction of Dr. Michel Brunet of the University of Poitiers. Struck by the skull's unusual mix of apelike and evolved hominid features, the discoverers assigned it to an entirely new genus and species — Sahelanthropus tchadensis. It is more commonly called Toumai, meaning "hope of life" in the local language. About a million years older than any previously recognized hominid, Toumai lived close to the time that molecular biologists think was the earliest period in which the human lineage diverged from the chimpanzee branch. The next oldest hominid appears to be the 6-million-year-old Orrorin tugenensis, found two years ago in Kenya but not yet fully accepted by many scientists. After it is Ardipithecus ramidus, which probably lived 4.4 million to 5.8 million years ago in Ethiopia.

Scientists suggest several possible explanations. Toumai could somehow be an ancestor of modern humans, or of gorillas or chimps. It could be a common ancestor of humans and chimps, before the divergence. With new fossil discovery, fossil hunters are more likely to find something unrelated directly to living creatures — more side branches to tangle the evolutionary bush. So the picture of human genealogy gets more complex, not simpler.

Although overshadowed by the news of Toumai, the well-preserved 1.75-million-year-old skull from Georgia, Europe, was also full of surprises, in this case concerning a later chapter in the hominid story. It raised questions about the identity of the first hominids to be intercontinental travelers, who set in motion the migrations that would eventually lead to human occupation of the entire planet.

The discovery, reported in the July 5 issue of the journal Science, was made at the medieval town Dmanisi, 50 miles southwest of Tbilisi, the Georgian capital. Two years ago, scientists announced finding two other skulls at the same site, but the new one appears to be intriguingly different and a challenge to prevailing views. Scientists have long been thought that the first hominid out-of-Africa migrants were Homo erectus, a species with large brains and a stature approaching human dimensions. The species was widely assumed to have stepped out in the world once they evolved their greater intelligence and longer legs and invented more advanced stone tools.

Homo Ergaster

Homo ergaster is an extinct chronospecies of Homo that lived in eastern and southern Africa during the early Pleistocene, about 1.9 years ago. There is still disagreement on the subject of the classification, ancestry, and progeny of H. ergaster, but it is now widely accepted to be the direct ancestor of later hominids such as Homo heidelbergensis, Homo sapiens, and Homo neanderthalensis rather than Asian Homo erectus. It is one of the earliest members of the genus Homo, possibly descended from, or sharing a common ancestor with, Homo habilis.

Homo ergaster is believed to have diverged from the lineage of H. habilis between 1.9 and 1.8 million years ago; the lineage that emigrated Africa and fathered Homo erectus diverged from the lineage of H. ergaster almost immediately after this. These early descendants of Homo ergaster may have been discovered in Dmanisi, Georgia. Homo ergaster remained stable for around 500,000 years in Africa before disappearing from the fossil record around 1.4 million years ago. No identifiable cause has been attributed to this disappearance; the later evolution of the similar Homo heidelbergensis in Africa may indicate that this is simply a hole in the record, or that some intermediate species has not yet been discovered.

Homo ergaster used more diverse and sophisticated stone tools than its predecessor, Homo habilis, developing the first Acheulean bifacial axes. The use of Acheulean tools began approximately 1.6 million years ago, the line of Homo erectus diverged some 200,000 years before the general innovation of Acheulean technology. Thus the Asian migratory descendants of Homo ergaster made no use of any Acheulean technology. Sexual dimorphism in Homo ergaster is greatly reduced from its australopithecine ancestors, but still greater than dimorphism in modern humans. This diminished competition for mates between males. Not only was Homo ergaster like modern humans in body, but also more in organisation and sociality than any earlier species. It is conceivable that Homo ergaster was the first hominin to harness fire: whether as the containment of natural fire, or as the lighting of artificial fire, is still a matter of contention.

Homo Rudolfensis

Homo rudolfensis was a bipedal hominid whose fossilized remains were discovered by Bernard Ngeneo, a member of a team led by anthropologist Richard Leakey and zoologist Meave Leakey in 1972, at Koobi Fora on the east side of Lake Rudolf (now Lake Turkana) in Kenya. The scientific name Homo rudolfensis was proposed in 1986 by V. P. Alekseyev for the specimen Skull 1470 (KNM ER 1470). Skull 1470 has an estimated age of 1.9 million years.

Originally thought to be a member of the species Homo habilis, the fossil was the center of much debate concerning its species. Assigned initially to Homo habilis, the skull was at first incorrectly dated at nearly three million years old. The differences in this skull, when compared to others of the Homo habilis species, are too pronounced, leading to the presumption of a Homo rudolfensis species, contemporary with Homo habilis. It is not certain if H. rudolfensis was ancestral to the later species in Homo, or if H. habilis was, or if some third species yet to be discovered was.

In March 2007, a team led by Timothy Bromage, an anthropologist at New York University, reconstructed the skull of KNM-ER 1470. The new construction looked very ape-like (possibly due to an exaggerated rotation of the skull) and the cranial capacity based on the new construction was reported to be downsized from 752 cm³ to about 526 cm³, although this seemed to be a matter of some controversy. Bromage published his results in 2008 where the cranial capacity was now estimated at 700 cm³. Bromage said his team’s reconstruction included biological principles not known at the time of the skull’s discovery, which state that a mammal’s eyes, ears and mouth must be in precise relationships relative to one another.

Neanderthal Man a Smart Innovator

Neanderthal man was not as stupid as has been made out says a new study published by a University of Leicester archaeologist. In fact Neanderthals were far removed from their stereotypical image and were innovators, says Dr Terry Hopkinson of the School of Archaeology and Ancient History.

Neanderthals were the sister species of Homo sapiens, our own species, and inhabited Europe in the Middle Palaeolithic period which began some 300,000 years ago. This period has widely been thought to have been unremarkable and undramatic in cultural or evolutionary terms.

Now Dr Hopkinson has challenged this notion and shown that it does not fit the archaeological evidence. He says early Neanderthals were innovators as they devised new stone tool technologies and also coming to terms with ecological challenges that defeated their immediate ancestors, Homo heidelbergensis.

Conventional theories focus on tool innovation much later on leading up to the period when modern humans replaced Neanderthals some 40,000 years ago. Dr Hopkinson said: "There has been a consensus that the modern human mind turned on like a light switch about 50,000 years ago, only in Africa. But many ‘modern’ traits like the use of grind stones or big game hunting began to accumulate 300,000 years ago. In Europe the Neanderthals were gradually accumulating skills and tool manufacturing knowledge, stimulating cortical motor areas in the frontal lobe of the brain.

Not only did the Neanderthals combine old stone tool technologies in innovative ways to create new ways of working stone, says Dr Hopkinson. They also spread from western Europe into areas of central and eastern Europe their forbears had been unable to settle.

"The eastern expansion shows that the Neanderthals became capable of managing their lives and their landscapes in strongly seasonal environments,” said Dr Hopkinson.

Dr Hopkinson concludes:” Neanderthals have typically been thought of as incapable of innovation, as it was assumed to be something unique to Homo sapiens. With this evidence of innovation it becomes difficult to exclude Neanderthals from the concept of humanity."

Multiregional Origin of Modern Humans

The multiregional origin of Homo Sapiens, or modern humans, is a scientific theory proposed by Milford H. Wolpoff in 1988. It gives an explanation for the pattern of human evolution. The Multiregional origin theory holds that Homo erectus, Neanderthals, Homo sapiens and other humans were a single species. This species arose in Africa two and half million years ago as Homo erectus and then spread out over the world, developing adaptations to regional conditions, evolving worldwide to modern Homo sapiens.

A competing theory, the recent African origin of modern humans (also known as "Out of Africa"), has emerged as the near consensus view since the 1990s, proposing that modern humans arose in Africa around 100-200,000 years ago, moving out of Africa around 50-60,000 years ago to replace existing human species such as Homo erectus and the Neanderthals. But this theory is rather flimsy since it does not account for the fact that recent genetical studies conducted by German scientists in 2010 proved that modern humans share up to 6% of genes with the Neantherthal, suggesting that interbreeding took place with Homo sapiens sapiens between roughly 80,000 to 50,000 years ago.

Multiregional origin proponents claim that the discovery of hybrid Homo sapiens X neanderthalensis fossils in Israel and at the Abrigo do Lagar Velho rock-shelter site in Portugal in 1983 and 1999 respectively, further supports the multiregional hypothesis, by reflecting the admixture of diverse human populations.

Tungurahua

Tungurahua is an active 5,023m-high andesitic-dacitic stratovolcano which lies in the Andes Central Range of Ecuador. Towering more than 3 km above its northern base, this steep-sided mountain is one of Ecuador's most active volcanoes, giving its name to the province of Tungurahua. Volcanic activity restarted in 1999 and is still going on as of 2010 with major eruptions on August 16, 2006, 6 February 2008, and 28 May 2010. Tungurahua is Quichua word which means "Throat of Fire."

Three major volcanic edifices have been sequentially built up since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano, Tungurahua III, was constructed. Historical eruptions have all originated from the summit crater. They have been accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Ojos del Salado

Ojos del Salado is a massive 6,891m-high stratovolcano located in the Andes, on the Argentina-Chile border. It is the highest volcano in the world and the second highest mountain in the Western Hemisphere. Ojos del Salado is situated about 600 kilometers (370 miles) north of Aconcagua, the highest mountain in the Western Hemisphere at 6,959 m (22,841 ft).

Due to its location near the Atacama desert, the Ojos del Salado has very dry conditions with snow only remaining on the peak during winter. Despite the generally dry conditions, there is a permanent crater lake about 100 metres (300 ft) in diameter at an elevation of 6,390 m (20,960 ft) on the eastern side of Ojos del Salado. This is most likely the highest lake of any kind in the world.

The ascent of Ojos del Salado is mostly a hike except for the final section to the summit which is a difficult scramble that may require ropes. The first ascent was made in 1937 by Jan Alfred Szczepanski and Justyn Wojsznis, members of a Polish expedition in the Andes. Its name comes from the enormous deposits of salt that, in the form of lagoons or “eyes”, appear in its glaciers.

Ojos del Salado is a recently active volcano. The most recent known eruption was around 1300 years ago. However, there is also some evidence for a minor ash emission in 1993, which would definitely qualify the volcano as historically active. The presence of fumaroles high on the mountain and recent-looking lava flows, albeit of uncertain age, also argues in favor of a categorization as "active."

The first men to successfully climb Ojos del Salado were Polish mountaineers Jan Alfred Szczepanski and Justyn Wojsznis, getting to the summit on February 26, 1937.

Caichinque

Caichinque is a Pleistocene-Holocene volcanic complex which is located in the high Andean plateau of the Antofagasta Region, in Chile, between Salar de Talar and Salar de Capur. It lies southwest of the Salar de Atacama, directly S of Cerro Miñiques and SE of Cordón Puntas Negras forming part of the main branch of the Andean volcanic chain in this area.

More than a half dozen vents produced andesitic-to-dacitic lava flows, with young flows descending to the NE and SE from the 4450m-high summit of Caichinque. One prominent flow traveled 6 km to the east, forming two lobes extending into the Salar Talar. Route CH-23 is an approach road to the volcano area.

Batholith

A batholith is a large emplacement of igneous intrusive rock that forms from cooled magma deep in the earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock-types, such as granite, quartz monzonite, or diorite. A batholith is an exposed area of mostly continuous plutonic rock that covers an area larger than 100 square kilometers. Areas smaller than 100 square kilometers are called stocks. However, the majority of batholiths visible at the surface have areas far greater than 100 square kilometers. These areas are exposed to the surface through the process of erosion accelerated by continental uplift acting over many tens of millions to hundreds of millions of years. This process has removed several tens of square kilometers of overlying rock in many areas, exposing the once deeply buried batholiths.

A batholith is formed when many plutons converge to form a huge expanse of granitic rock. Some batholiths are mammoth, paralleling past and present subduction zones and other heat sources for hundreds of kilometers in continental crust. One such batholith is the Sierra Nevada Batholith, which is a continuous granitic formation that makes up much of the Sierra Nevada in California. An even larger batholith, the Coast Plutonic Complex is found predominantly in the Coast Mountains of western Canada, and extends for 1,800 kilometers and reaches into southeastern Alaska.

Batholiths may appear uniform, but they are in fact structures with complex compositions. They are composed of multiple bodies of igneous rock of irregular dimensions, typically at least several kilometers, that can be distinguished from adjacent igneous rock by some combination of criteria including age, composition, texture, or mappable structures. Individual plutons are crystallized from magma that traveled toward the surface from a zone of partial melting near the base of the Earth's crust.

El Solo Volcano

El Solo is a stratovolcano on the border between Argentina and Chile, west of Ojos del Salado. Lying in the Andes Mountain Range, it consists of nine eruptive centers and is covered in light-colored rhyodacite pyroclastic flow deposits. El Solo is 6190-m-high and was the source of major rhyodacitic pyroclastic-flow deposits erupted during the Holocene that thickly fill adjacent valleys.

Lithophysa

A lithophysa is a spherulitic bubble or cavity found in felsic volcanic rocks and glassy basalts and certain rhyolites. It is believed to be caused by expanding gases in tuffs before solidification. If it has become lined with crystals it may be referred to as a geode or a thunderegg. The word lithophysa is from the Latin for rock bubble. The term vug is also used for similar cavities although vug is usually restricted to mean cavities in rocks formed by the removal of material such as soluble minerals.

Maipo Volcano

Maipo is a 17,270ft-high stratovolcano that is situated in the Andes Mountain Range, lying on the border between Argentina and Chile. It is located 90 km (55 miles) south of Tupungato and about 100 km (60 miles) southeast of Santiago. Maipo volcano retains a symmetrical, conical volcanic shape, unlike many of the other nearby peaks, making it the best known peak in the region, though it is not the highest.

Maipo is located within the Diamante Caldera, a feature of about 15 km by 20 km size that is about one-half million years old. It rises about 1,900 m (6,230 ft) above the floor of the caldera. Immediately to the east of the peak, on the eastern side of the caldera floor, is Laguna del Diamante, a picturesque lake that formed when lava flows blocked drainage channels from the caldera in 1826. The Diamante Caldera erupted 450 cubic kilometers (108 cu mi) of tephra, 450 ka.

The region's climate is transitional between the drier Mediterranean climate of the peaks to the north and the cold, moist climate of Chilean Patagonia. Hence, while less glaciated than Patagonia, it has more permanent snow (on the wet, Chilean side) than peaks of similar elevation to the north.

Socompa

Socompa is a 6051m-high dacitic stratovolcano lying in the Andes Mountain Range, in the province of Salta, on the border of Argentina and Chile. It is best known for its large debris avalanche deposit, which is widely accepted as the best-preserved example of this type of deposit in the world, and also notable as the home of the world's most elevated known microbial ecosystems.

The western rim of Socompa volcano is bounded by the Monturaqui Basin, which is draped with the aforementioned deposit. Escondida Mining currently has a network of roads throughout this area, from beneath which they pump ground water for use at the nearby copper mine. The southern margin of the deposit is bordered by the Antofagasta to Salta trans-Andean railway, although this is rarely used.

Socompa is difficult to reach - either from the north along dirt tracks south of the Miscanti Pass, or from the west via the Escondida copper mine. Both routes require a full-day's driving and for any reasonable amount of time to be spent at Socompa would need significant planning.

Lanin Volcano

Lanin is a 12,293ft-high, cone-shaped stratovolcano on the border of Argentina and Chile. It is part of two national parks: Lanín in Argentina and Villarrica in Chile. It is a symbol of the Argentine province of Neuquén, being part of its flag and its anthem. Although the date of its last eruption is not known, it is estimated to have occurred within the last 10,000 years.

The ascent is regulated by the management of Argentine National Parks and the Argentine National Gendarmerie, and is relatively simple, but many deaths have occurred due to lack of responsibility and caution of the climbers. The nearest towns, usually employed as a base for climbers, are Pucón in Chile and Junín de los Andes in Argentina.

There are two paths to the summit: one on the north, starting at 1,200 above mean sea level near Lake Tromen and the international Mamuil Malal Pass, accessible via Neuquén's Provincial Route 60; and one on the south, starting beside Lake Huechulafquen, accessible via Provincial Route 61.

Krakatoa Volcano

Krakatoa is a volcano in the Sunda Strait between the islands of Java and Sumatra in Indonesia. The best known eruption of Krakatoa culminated in a series of massive explosions on August 26–27, 1883, which was among the most violent volcanic events in modern and recorded history. With a Volcanic Explosivity Index (VEI) of 6, the eruption was equivalent to 200 megatons of TNT (840 PJ)—about 13,000 times the nuclear yield of the Little Boy bomb (13 to 16 kT) that devastated Hiroshima, Japan during World War II and four times the yield of the Tsar Bomba (50 MT), the largest nuclear device ever detonated.

The 1883 eruption ejected approximately 21 cubic kilometres (5.0 cu mi) of rock, ash, and pumice. The cataclysmic explosion was distinctly heard as far away as Perth in Western Australia, about 1,930 miles (3,110 km) away, and the island of Rodrigues near Mauritius, about 3,000 miles (5,000 km) away. Near Krakatau, according to official records, 165 villages and towns were destroyed and 132 seriously damaged, at least 36,417 (official toll) people died, and many thousands were injured by the eruption, mostly from the tsunamis that followed the explosion. The eruption destroyed two-thirds of the island of Krakatoa.

Eruptions at the volcano since 1927 have built a new island in the same location, named Anak Krakatau (Indonesian: "Child of Krakatoa"). This island currently has a radius of roughly 2 kilometres (1.2 mi) and a high point around 300 metres (980 ft) above sea level, growing 5 metres (16 ft) each year.

Phreatic Eruption

A phreatic eruption is a type of volcanic eruption which occurs when rising magma makes contact surface water. The extreme temperature of the magma (anywhere from 600 to 1,170 °C) causes near-instantaneous evaporation to steam resulting in an explosion of steam, water, ash, rock, and volcanic bombs. At Mount St. Helens hundreds of steam explosions preceded a 1980 plinian eruption of the volcano. A less intense geothermal event may result in a mud volcano. In 1949, Thomas Jaggar described this type of activity as a steam-blast eruption.

Phreatic eruptions typically include steam and rock fragments; the inclusion of lava is unusual. The temperature of the fragments can range from cold to incandescent. If molten material is included, the term phreato-magmatic may be used. These eruptions occasionally create broad, low-relief craters called maars. Phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas emissions. The former can asphyxiate at sufficient concentration; the latter is a broad spectrum poison. A 1979 phreatic eruption on the island of Java killed 149 people, most of whom were overcome by poisonous gases.

It is believed the 1883 eruption of Krakatoa, which obliterated most of the volcanic island and created the loudest sound in recorded history, was a phreatic event. Kilauea, in Hawaii, has a long record of phreatic explosions; a 1924 phreatic eruption hurled rocks estimated at eight tons up to a distance of one kilometer. Additional examples are the 1963–65 eruption of Surtsey, the 1965 eruption of Taal Volcano, and the 1982 Mount Tarumae eruption.

Hydrothermal Circulation

Hydrothermal circulation is the circulation of hot water underneath the earth. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. It usually occurs near volcanic activity, but can occur in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism. The word "hydrothermal" derives from Greek: "Hydros" means water and "thermos" means heat.

Hydrothermal circulation in the oceans is the passage of the water through mid-oceanic ridge systems. The term includes both the circulation of the well known, high temperature vent waters near the ridge crests, and the much lower temperature, diffuse flow of water through sediments and buried basalts further from the ridge crests.

Hydrothermal circulation is not limited to ocean ridge environments. The source water for geysers and hot springs is heated groundwater convecting below and lateral to the hot water vent. Hydrothermal circulating convection cells exist any place an anomalous source of heat, such as an intruding magma or volcanic vent, comes into contact with the groundwater system.