Hydrothermal circulation is the circulation of hot water underneath the earth. It is located most often in the vicinity of sources of heat within the Earth’s crust. It usually occurs near volcanic activity, but can also 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.
Origin of The Andes
The origin of the Andes Mountains Range goes back to 50 million years ago, to the Tertiary period of the Cenozoic Era. This long chain of massive geological elevation originated by the collision of the Nazca tectonic plate against the South American plate about 50 million years ago. The portion of the Andes with highest peaks in the American continent makes the border between Argentina and Chile. Aconcagua is 6,959 m high.
This geological phenomenon of collision of plates, which gave rise to all mountain ranges in the world, is called subduction movement, which occurs at a convergent boundary between two tectonic plates of the lithosphere. To sum up, the origin of the Andes mountains is the result of a collision of plates, with the Nazca plate sliding underneath the South American one, lifting geological materials up to great heights and folding them up amid intense volcanic activities.
This slow geological process that formed the Andes range is still going on, causing strong earthquakes and sunamis in the Chilean and Peruvian coastal regions. During the orogenesis of the Tertiary, igneous rocks, such as granite, basalt, and quartz which are part of the western edge of the South American crystalline basement rock, were raised above 6,000 m of altitude. The Tertiary is a geological period of Cenozoic Era.
Below, a picture of the Andes Mountains in Patagonia, Argentina, near the Chilean border.
Below, a map showing the world’s tectonic plates, with the convergent movement of the Nazca against the South American Plate marked with a red line.
Geographical Features
Geographical features are all those natural formations of the planet Earth’s surface which form the landscapes of a country. All these formations, which are characteristics of any given region of the world, have names in geography; they are the mountains, plains, plateau, valleys, rivers, lakes, seas, oceans, etc. All these features have been shaped by natural phenomena, such as rain, winds, volcanoes, and especially geological movement of tectonic plates of the Earth over millions of years.
Mountains can be geologically new or old as they are usually arranged in chains, which are called range, like the Andes mountain range in South America. If the system of mountains is new, they can be very high and the mountains have snow-capped peaks, with the tallest ones being called mounts, which are abbreviated “Mt.”, such as Mt Everest in Asia, or Mt Aconcagua in South America. A chain of mountains usually constitute a divide or water shed, determining the direction in which water streams flow, sometimes being the natural boundaries or borders between countries.
Valleys are limited open spaces, often with grassy land, surrounded by chains of mountains. They are usually wide enough to be inhabited by human beings and ruminants. A valley is emptied by a main river and its creek-like tributaries, whose water originates from melting snow on top of mountain peaks. It is usually communicated with a wide open plain through a ravine or gorge.
Rivers can be large and small, flowing into oceans, seas or large hollow areas called depressions, forming lakes. Large rivers are fed by other important water streams, which are called tributaries. A large region drained by a big river and its tributaries is called basin. Rivers can be created by rain water or by the melting of snow in the mountains, or by both. The largest river in the world is the Amazon, which originates from the union of snow-melting streams in the Andes, in Peru.
Plains are large areas of flat land, usually covered by rich, black sediments where grass grow and large herds of ruminants thrive. The black sediment, the top layer of plains, are geologically new in the Earth history. They can be referred to as savannas, prairies, steppes, or grasslands. There are famous plains, such as the Pampas (Argentina), the Great Plains (USA), and the Aquitaine (France).
Oceans and seas are large masses of salt water covering the the lowest parts of the Earth surface. They account for about 70% of the planet’s surface. Life began in the oceans as primitive prokaryotic cells, most of them being cyanobacteria.
Below, on of many geographical features, a grassy plain; here a Central Asia grassy steppe, which is very fit for animal husbandry. The nomadic tribes have been its main inhabitants.
Types of Deformation
There are two types of deformation in the lithosphere, according to the morphology of the Earth’s continents. They are orogeny and epeirogeny. The former has taken place recently, between 45 and 50 million years ago, and it is still going on, while the latter dates back to the Proterozoic era, having begun about 4 billion years ago.
Orogeny is the deformation of the Earth crust through the mountain-building process, which involves the violent collision of two tectonic plates and the ejection of molten rocks that are uplifted as they get solidified. This dynamic geological process comprises faulting, folding, strong seismicity, and a linear mountain chain of high-altitude sharp peaks. It is relatively new, from the Tertiary period of the Cenezoic era. An example of orogeny is the Andes mountain range in South America, which is the product of the South American plate and the Nazca plate collision as it is 47 million years old. The word orogeny derives from Greek, with oros meaning ‘mountain’, and –geny, ‘genesis’ (creation, development).
Epeirogeny is the broad and slow warping of the lithosphere. It does not involve local intense folding, faulting; nor is there seismicity. This type of deformation has given way to plains (due to erosion), to the emergence of plateaus, as well as large areas of depression. Sometimes these geographical features are surrounded by very old, low mountains. The cratons are examples of this process, such as the Guayana’s Highlands in Venezuela and Brazil. Granite and basalt rock outcrops and the absence of seismicity are two common features of epeirogeny. Thus, it only occurs in stable and solidified portions of the Earth’s crust. Also from Greek, with epeiros meaning ‘continent’, and -geny, ‘genesis’.
CO2 Levels in Geologic History
The charts of CO2 levels in geologic history show you clearly that today’s carbon dioxide levels are some of the lowest, with 400 ppm (parts per million), especially if you compare it with those of the Paleozoic and Mesozoic Era. Today’s levels might be higher than the 1980s but they are still very low. You can see that during the Cambrian period of the Paleozoic Era, it was at the highest, with almost 7,000 ppm. When the CO2 levels were between 4,500 and 4,000, there was a massive proliferation of terrestrial plants and animal lives, with the appearance of the amphibians and primitive reptiles during the Devonian and Carboniferous period, respectively.
Not only did the quantity of carbon dioxide was much higher during the Paleozoic and Mesozoic than today’s levels but also the amount of nitrogen in the atmosphere was much, much higher than it is today, yet animals could still breathe, live, and thrive as there was enough oxygen for every living creature and enough CO2 for every plant. In the geological history of the Earth, CO2, oxygen, and nitrogen levels rose and fell without the existence of human beings and human industry.
During the Permian, the last period of the Paleozoic, the CO2 levels dropped sharply to about 700 ppm. However, the amount of carbon dioxide rose up steeply to about 2,100 and 2,500 ppm as animal and tropical plants flourished again, with the emergence and abundance of the dinosaurs during the Triassic and Jurassic respectively; also the first mammals appeared during the Cretaceous period. During the first part of the Cenozoic Era, they still remain high between the Paleocene and Eocene epoch at 2,200 and 1,700 ppm. Yet, at these high levels of carbon dioxide, mammals thrived and scattered to every corner of the planet. Then CO2 dropped sharply at the end of the Eocene and the beginning of the Oligocene. This coincided with a general cooling of the Earth temperatures and the disappearance of large tracts of rain forests, giving way to the emergence of the huge grassy plains, such as the African savanna, and the Caucasian, Russian, and Mongolian steppes. Abundant grass (Gramineae) boosted the thrive of ruminants (cattle, deer, sheep, buffalo, etc.) and equines; and with them carnivores flourished.
Below, the CO2 levels during the Cenozoic.
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