what types of volcanic eruptions causes a cooling effect?
what types of volcanic eruptions causes a warming effect?
list gases involved for each.
Answers
When volcanoes erupt, they emit a mixture of gases and particles into the air. Some of them, such as ash and sulphur dioxide, have a cooling effect, because they (or the substances they cause) reflect sunlight away from the earth. Others, such as CO2, cause warming by adding to the the greenhouse effect.
The cooling influence is particularly marked in the case of large eruptions able to blast sun-blocking particles all the way up to the stratosphere – such as Mount Pinatubo in 1991, which caused a significant dip in global temperatures in the following year or two. It's difficult to know for sure that the cooling observed after a particular eruption is definitely the result of that eruption, but examining the average global temperature change after multiple eruptions proves a strong link.
As for greenhouse gases, underwater and land-based volcanoes are estimated to release, in total, around 100–300 million tonnes of CO2 each year, according to the British Geological Survey and the US Geological Survey. That's a large quantity, but only around 1% of the amount that humans release from burning fossil fuel alone.
As a rule, the cooling influence of an individual volcano will dominate for the period immediately after the eruption but the warming impact will last much longer. So the significance of each depends on the timeframe being considered. A very large volcano in 2011 may significantly reduce temperatures in 2012 but slightly warm them in 2100.
It has sometimes been suggested by those who seek to disprove human impact on the climate that volcanoes release more CO2 than human activity. This is simply incorrect. As the British Geological Survey puts it:
"The contribution to the present day atmospheric CO2 loading from volcanic emissions is … relatively insignificant."
Some of the eruptive structures formed during volcanic activity (counterclockwise): a Plinian eruption column, Hawaiian pahoehoe flows, and a lava arc from a Strombolian eruption.
Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.
There are three different types of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The third eruptive type is the phreatic eruption, which is driven by the superheating of steam via contact with magma; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock.
Within these wide-defining eruptive types are several subtypes. The weakest are Hawaiian and submarine, then Strombolian, followed by Vulcanian and Surtseyan. The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions; the strongest eruptions are called "Ultra-Plinian." Subglacial and phreatic eruptions are defined by their eruptive mechanism, and vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index (VEI), an order of magnitude scale ranging from 0 to 8 that often correlates to eruptive types.
Eruption mechanisms
Diagram showing the scale of VEI correlation with total ejecta volume.
Volcanic eruptions arise through three main mechanisms:[1]
Gas release under decompression causing magmatic eruptions
Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions
Ejection of entrained particles during steam eruptions causing phreatic eruptions
There are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels magma and tephra.[1] Effusive eruptions, meanwhile, are characterized by the outpouring of lava without significant explosive eruption.[2]
Volcanic eruptions vary widely in strength. On the one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows, which are typically not very dangerous. On the other extreme, Plinian eruptions are large, violent, and highly dangerous explosive events. Volcanoes are not bound to one eruptive style, and frequently display many different types, both passive and explosive, even in the span of a single eruptive cycle.[3] Volcanoes do not always erupt vertically from a single crater near their peak, either. Some volcanoes exhibit lateral and fissure eruptions. Notably, many Hawaiian eruptions start from rift zones,[4] and some of the strongest Surtseyan eruptions develop along fracture zones.[5] Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years. But Columbia University volcanologists found that the eruption of Costa Rica’s Irazú Volcano in 1963 was likely triggered by magma that took a nonstop route from the mantle over just a few months.