It is estimated that over 500 million people throughout the world live near an active volcanic hazard place. All of those people are susceptible to a variety of different volcanic hazards.
Natural disasters can have truly devastating consequences but only a strong volcanic eruption in the right place can have consequences for everyone everywhere. But why do volcanoes even exist? Where do they come from and why are some different from others.
Let’s get into the different types of volcanic hazards.
Different types of volcanic hazards
Volcanoes predictably exist where oceanic plates meet continental plates but what processes caused this as an oceanic plate subducts beneath a continental plate. It experiences both an increase in temperature and pressure.
The composition of the subducting lithosphere isn’t much different from the asthenosphere. So this heat and pressure increase shouldn’t be much of an issue but during subduction.
The lithosphere brings with it contaminants other than just the silicon, oxygen, and cations forming up their structure. The two primary contaminants we are concerned about within this process are water and carbon dioxide.
We’ll look at the example of salt in water. When we freeze water, the molecules within are organized to form this solid lattice structure. Now if we imagine a contaminant like a salt ion, this disrupts potential hydrogen bonds.
The nearby water molecules detach and remain liquid. Not only can they form pseudo ionic bonds with this ion but their mingling also increases. The average amount of hydrogen bonds they can create thus producing more stability.
This principle holds true to any contaminant in any material. As the contaminant disrupts their lattice structure, the molecules in a material can achieve more stability by interacting in their liquid form than remaining in their solid form.
Thus contaminants cause a breakdown in lattice structure quicker or in other words lower the melting point. As the pressure and temperature increase, the water and CO2 molecules within the lithosphere enter their gas phase.
But due to the extreme pressure, there’s nowhere for them to go. So these contaminants stick around and disrupt the lattice structure of the lithosphere material. This causes it to melt into a semi-liquid phase.
Since liquids are less dense than solids, this semi-liquid magma slowly begins to rise back up towards the surface. Eventually, the magma will reach the Moho discontinuity or the bottom of the crust-mantle.
The buoyant forces pushing the magma to the surface weaken and as a result, the vast majority of forms of magma begin to pool up. In fact, most magma never reaches the surface.
It simply solidifies and crystallizes mixing with the surrounding material. If however, enough magma pulls up underneath, the upwards force can cause enough stress on the crust because cracks and fissures form at which point our magma can continue to rise. This process creates magma on tectonic plate boundaries.
Pyroclastic flows
These are hot gases that are infused with hot molten ash and larger fragments. These move at a pretty rapid speed of 60 miles an hour. So they’re typically broken into two parts.
There’s a low-density cloud of expanding gases with ash and we have a ground-hugging portion that’s mostly vesicular material. So gas is escaping from that as well.
Lahars
These are mudflows that contain volcanic debris and water. These travel at speeds of 30 kilometers an hour or 20 miles an hour and volcanoes do not need to erupt to trigger a lahar.
A lot of people want to know where the water comes from. Only talk about lahars. Well, think of the Cascades in America and up through Canada. Most of them are snowcats.
As lava or magma is approaching the surface it’s heating that up. It’s starting to melt. It’s gonna mix with that debris and it creates an out-of-control mudflow.
Also, you can read: Different types of Volcanic eruptions and Volcanic gases
Tsunamis
We have volcanoes and then we have some earthquake-related ones to tsunamis that are usually caused by strong earthquakes due to a volcanic eruption. Volcanic ash over 80 plus commercial flights are damaged by flying through clouds of volcanic ash each year.
Now with all the volcanoes in Iceland erupting this has been more in the news now than what it has been lately.
Volcanic gases
Volcanic gases can affect your respiratory health because they can release poisonous gases that kill people and animals. Now it does have some effects on the weather.
This combination actually reflects sunlight causing the earth to cool. So I’ve given an example of Mount Pinatubo and the sulfur dioxide.
So you see that it was over ten parts per billion which doesn’t seem like a lot but it was elevated and it created the stream and it was carried by the jet stream and it reflected sunlight and it caused a cooling effect.
Most volcanoes are going to be located along the margins of our ocean basins and then some other general locations include our deep ocean basins and the interiors of our continents.
Extra heat makes a section of the mantle less dense, which then causes it to rise normally. The temperatures within the mantle would be enough to melt it, but the extreme pressure prevents this.
However, as the warm section of the mantle rises, pressure decreases causing decompressive melting into a more liquid composition. As a result, it becomes even less dense and rises even faster.
The coolest thing about hot spots is that you can see the path, a tectonic plate traveled above it as the column underneath it continually poked. Why are some volcanoes effusive and others explosive?
This property is tied to gas content in the magma. Just like a carbonated beverage, the gas would like to leave. But it’s held in place by the pressure surrounding it. So very similar to opening a shaken beverage.
If the pressure is suddenly reduced like the rupturing of an overhead Rock ceiling, this decrease in pressure causes gas to escape and expand from the lava. The expansions inevitably expose more lava to the air which causes more gas to escape causing more expansion and so on.
Thus you have an explosion. So the more gas in magma, the more explosive it is. But what dictates the gas content of magma? This property is controlled by the Magma’s viscosity, strongly mafic or liquidy.
Magmas have very small solid fragments within them. Hence they behave like a liquid and interchange with their surroundings. However, very viscous and felsic magma have very large crystallization.
Zinc solid complexes within them make it more difficult for trapped gases to find. So the higher the silicon oxide content and subsequently the higher the viscosity. The more volatile ZAR gases can be trapped inside.
Therefore it is this highly viscous felsic magma that is responsible for the strong explosive eruptions. What kind of magma is formed as magma passes through and interacts with the overlying crust. It melts and incorporates a lot of the crust material within the magma itself.
Since roughly 90% of magma that reaches the surface forms in the ocean, most of it is of liquid mafic composition. Earlier we mentioned that two oceanic plates can meet up and whichever plate is denser will subduct underneath to form magma.
As a result, the rising magma interacts with the mafic ocean crust. Therefore volcanic islands like the Galapagos and the Aleutians all formed from mafic magma and experienced effusive eruptions.
However when magma rises through and interacts with continental crust, not only is continental crust thicker, but it also has a high silicon content incorporating. The silicon makes the magma more felsic and thus more viscous.
An easy way to determine the eruption type of a volcano is by its shape. Steeper volcanoes or stratovolcanoes generally are explosive whereas shield volcanoes with low grades and wide bases are effusive.
Stratovolcanoes are of utmost importance because they can send cubic kilometers worth of material into the stratosphere while suspended at high altitudes. This material reduces solar insulation and subsequently cools the entire planet.
Paleoclimatologists believe that ancient volcanoes roughly 250 million years ago caused the worst mass extinction scene. This resulted at the end of the Paleozoic era and a little over 200 years ago the Tambora eruption caused massive food shortages in Europe.
Igneous activity at convergent plate boundaries
This is a pretty common plate boundary where we’re gonna get volcanic eruptions. Oceanic crust descends into the mantle. Remember it is denser so it’s going down. As it’s going down it reaches the mantle.
It is going to start to melt and as it melts magma will slowly rise up. It can form volcanic island arcs in the ocean or it can produce continental volcanic arcs on the continent. Talking about the Ring of Fire and economic minerals, we have a poor free Compro copper type deposit.
Remember poor free rocks have two different sizes of mineral grains. We have the phonetic and then we have the theater, Riddick. It creates phenocryst and ground mats and then we can get copper and gold.
We can get the same with just copper and then we can get at B thermal which can have silver. It can have gold and you can just see how those different volcanic places can be related to important economic minerals.
Partial melting of the mantle rocks is occurring because releasing confining pressure lowers the melting temperature.
We have large quantities of basaltic magma that are produced. We also get intraplate igneous activity. Activity within a rigid plate. So we will have plumes of hot mantle material that are sitting toward the surface.
These form localized volcanic regions called hotspots and this can be associated with our Hawaiian Islands.