Tectonic–climatic interaction is the interrelationship between tectonic processes and the climate system. The tectonic processes in question include orogenesis, volcanism, and erosion, while relevant climatic processes include atmospheric circulation, orographic lift, monsoon circulation and the rain shadow effect. As the geological record of past climate changes over millions of years is sparse and poorly resolved, many questions remain unresolved regarding the nature of tectonic-climate interaction, although it is an area of active research by geologists and palaeoclimatologists.
Orographic controls on climate Depending on the vertical and horizontal magnitude of a mountain range, it has the potential to have strong effects on global and regional climate patterns and processes including: deflection of atmospheric circulation, creation of orographic lift, altering monsoon circulation, and causing the rain shadow effect.
One example of an elevated terrain and its effect on climate occurs in the Southeast Asian Himalayas, the world's highest mountain system. A range of this size has the ability to influence geographic temperature, precipitation, and wind. Theories suggest that the uplift of the Tibetan Plateau has resulted in stronger deflections of the atmospheric jet stream, a heavier monsoonal circulation, increased rainfall on the front slopes, greater rates of chemical weathering, and thus lower atmospheric concentrations. It is possible that the spatial magnitude of this range is so great that it creates a regional monsoon circulation in addition to disrupting hemispheric-scale atmospheric circulation.
The monsoon season in Southeast Asia occurs due to the Asian continent becoming warmer than the surrounding oceans during the summer; as a low-pressure cell is created above the continents, a high-pressure cell forms over the cooler ocean, causing advection of moist air, creating heavy precipitation from Africa to Southeast Asia. However, the intensity of the rainfall over Southeast Asia is greater than the African monsoon, which can be attributed to the awesome size of the Asian continent compared to the African continent and the presence of a vast mountain system. This not only affects the climate of Southeast Asia, but modifies the climate in neighboring areas such as Siberia, central Asia, the Middle East, and the Mediterranean basin as well. To test this a model was created that changed only the topography of current landmasses, which resulted in correlations between the model and global fluctuations in precipitation and temperature over the past 40 Myr. interpreted by scientists.
It is commonly agreed upon that global climate fluctuations are strongly dictated by the presence or absence of greenhouse gases in the atmosphere and carbon dioxide (CO2) is typically considered the most significant greenhouse gas. Observations infer that large uplifts of mountain ranges globally result in higher chemical erosion rates, thus lowering the volume of CO2 in the atmosphere as well as causing global cooling. This occurs because in regions of higher elevation there are higher rates of mechanical erosion (i.e. gravity, fluvial processes) and there is constant exposure and availability of materials available for chemical weathering. The following is a simplified equation describing the consumption of CO2 during chemical weathering of silicates:
CaSiO3 + CO2 ↔ CaCO3 + SiO2
From this equation, it is inferred that carbon dioxide is consumed during chemical weathering and thus lower concentrations of the gas will be present in the atmosphere as long as chemical weathering rates are high enough.
Climate-driven tectonism
There are scientists who reject that uplift is the sole cause of climate change and are in favor of uplift as a result of climate change. Some geologists theorize that a cooler and stormier climate (such as glaciations and increased precipitation) can give a landscape a younger appearance such as incision of high terrains and increased erosion rates. Glaciers are a powerful eroding agent with the ability to incise and carve deep valleys and when rapid erosion of the earth's surface occurs, especially in an area of limited relief, it is possible for isostatic rebound to occur, creating high peaks and deep valleys. A lack of glaciation or precipitation can cause an increase in erosion, but can vary between localities. It is possible to create erosion in the absence of precipitation because there would be a decrease in vegetation, which typically acts as a protective cover for the bedrock.
Models also suggest that certain topographic features of the Himalayan and Andes region are determined by an erosional/climatic interaction as opposed to tectonism. These models reveal a correlation between regional precipitation and a maximum topographic limit at the plateau margin. In the southern Andes where there is relatively low precipitation and denudation rates, there is no real extreme topography present at the plateau margin while in the north there are higher rates of precipitation and the presence of extreme topography.
Another interesting theory comes from an investigation of the uplift of the Andes during the Cenozoic. Some scientists hypothesize that the tectonic processes of plate subduction and mountain building are products of erosion and sedimentation. When there is an arid climate influenced by the rain shadow effect in a mountainous region, sediment supply to the trench can be reduced or even cut off. These sediments are thought to act as lubricants at the plate interface and this reduction increases the shear stress present at the interface that is large enough to support the high Andes.
Volcanism
Introduction Around the world, dotting the map are volcanoes of all shapes and sizes. Lining the landmass around the Pacific Ocean are the well-known volcanoes of the Pacific Ring of Fire. From the Aleutian Islands to the Andes Mountains in Chile, these volcanoes have sculpted their local and regional environments. Aside from admiring their majestic beauty, one might wonder how these geologic wonders work and what role they play in changing the landscape and atmosphere. Principally, volcanoes are geologic features that exude magmatic material from below Earth's surface onto the surface. Upon reaching the surface, the term "magma" disappears and "lava" becomes the common nomenclature. This lava cools and forms igneous rock. By examining igneous rocks, it is possible to derive a chain of events that led from the original melt of the magma to the crystallization of the lava at Earth's surface. By examining igneous rocks, it is possible to postulate evidence for volcanic outgassing, which is known to alter atmospheric chemistry. This alteration of atmospheric chemistry changes climate cycles both globally and locally.
Fundamentals of igneous rock and magmatic gas formation Magmas are the starting point for the creation of a volcano. In order to understand volcanism, it is critical to understand the processes that form volcanoes. Magmas are created by keeping temperature, pressure, and composition (known as P-T-X) in the realm of melt conditions. The pressure and temperature for melts are understood by knowing the chemistry of the melt. To keep magma in a melt condition, a change in one variable will result in the change of another variable in order to maintain equilibrium (i.e. Le Chatlier's Principle). The production of magma is accomplished in multiple ways: 1) subduction of oceanic crust, 2) creation of a hot spot from a mantle plume, and 3) divergence of oceanic or continental plates. The subduction of oceanic crust produces a magmatic melt usually at great depth. Yellowstone National Park is a hot spot located within the center of a continent. Divergence of continental plates (i.e. the Atlantic Mid-Ocean ridge complex) creates magmas very near the surface of the Earth. A plume of heat from the mantle will melt rocks, creating a hot spot, which can be located at any depth in the crust. Hot spots in oceanic crust develop different magmatic plumbing systems based on plate velocities. Hawaii and the Madeira Archipelago (off the West coast of Africa) are examples of volcanic complexes with two different plumbing systems. Because islands such as Hawaii move more quickly than Madeira, the layered rocks at Hawaii have a different chemistry than those at Madeira. The layers beneath Hawaii and Madeira are different because the magma produced underground at these locations rests for different amounts of time. The longer the amount of time magma will rest underground, the warmer the host rocks become. Fractionation of crystals from melt is partially driven by heat; therefore, the igneous rock produced will vary from an insulated host to a non-insulated host. Each of these avenues of magmatic creation develops different igneous rocks and, thus, various P-T-X histories. Definitions and other geologic explanations of igneous systems are explained in Loren A. Raymond's Petrology text.Raymond, Loren A., Petrology: The Study of Igneous, Sedimentary and Metamorphic Rocks. Waveland Press, Edition 2, May 30, 2007.
In order to understand the creation of igneous rocks from a melt, it is fundamental to understand the concepts produced by Drs. Norman Bowen and Frank Tuttle from the NaAlSiO4-KAlSiO4-SiO2-H2O system. Tuttle and Bowen accomplished their work by using experimental petrologic laboratories that produce synthetic igneous materials from mixes of reagents. Observations from these experiments indicate that as a melt cools, it will produce derivative magmas and igneous rock. Following Bowen's research, the magma will crystallize a mafic igneous rock prior to a felsic igneous rock. As this crystallization process occurs in nature, pressure and temperature decrease, which changes the composition of the melt along various stages of the process. This constantly changing chemical environment alters the final composition that reaches the Earth's surface.