We’re gonna talk about volcanic eruptions. Some factors that affect viscosity are the temperature. So hotter magmas are less viscous.
Which means they flow more. Composition by composition means silica content. High silica high viscosity. Which means it doesn’t flow. Low silica, more fluid. Gas content affects the Magma’s mobility.
Gases expand near the surface and are extruded. So when we’re talking about being more resistant to flow, the more resistant to flow is going to be an example of honey.
Well, less resistant to flow is going to be water. So for two examples, we have a quiet volcano in Hawaii and an explosive one Mount st. Volcano eruptions are more dangerous because it has more of these dissolved gases building and it has larger explosions.
Pahoehoe is a very runny material that resembles a twisted ropey texture. Aa is a term that we use for very rough jagged or blocky lava on the surface.
On the surface, most of the Earth’s volcanoes occur along ocean ridges or had been an ocean ridges. So we actually do find looking into the historic geology of these features you can find these pillow lavas.
Somewhere else like in the middle of a different state which then would help us kind of assume the fact that when they were deposited that they must have been near a margin of some sort with water.
So what happens is as material flows out it quickly solidifies because it’s getting cool because the water is cold and it forms this volcanic gas. It results in these numerous tube-like structures called pillow lavas.
The size range can be from everything from a powder to items larger than a car.
It kind of looks like a bunch of boba that’s merged together and they the obviously cool and turn into a harder material. So we actually have examples of this in several parts of California.
Different types of lava flow during Volcanic eruptions
When we look at volcanoes there are a lot of different materials involved, you know we can see that we have multiple different types of materials.
Some of the nature of volcanoes such as lava flows are very unique and different. So basaltic lavas make up about 90% of all lava on the surface that’s flowing fluid in its nature and they flow in sheets or streams like ribbons.
Now rhyolitic lava makes up only about 10%. They move very slowly and do not travel very far. We find in most rhyolitic makeups that are usually very thick layers that have just slowly merged out and created larger line deposits.
Pahoehoe lava
The first one is super fun to see. It is pahoehoe lava and it resembles braids and ropes. It’s hotter, more fluid. Pahoehoe lava flows develop into lava but you can’t have it the other way around and they can create lava tubes which are cave-like tunnels that are conduits that carry lava.
Aa lava
Now our next type of lava is pronounced as Ah-Ah. These are jagged blocks. Now the easiest way to tell the difference between a hoi and Ah-Ah is that Ah-Ah is gonna be so rough that if you were to touch it, it is going to be jagged and it’s gonna rip your hand up.
Black lava
These are vicious and acidic to rhyolitic lava and their short thick flows look similar to our ah-ah but the blocks have smoother surfaces.
Pillow lavas
These form along with oceanic lava flows. So what’s happening is that as the lava is coming up on the ocean floor it creates a little bulb and it starts to pool all around it. It’s eventually gonna break through one side. It creates another bulb.
Extruded materials
We will first learn about gases. So gases make up about 1 to 6 percent of the Magma’s total weight but thousands of tons of gases can be omitted daily. The type of gases emitted varies from place to place.
What is the role of gases in an eruption? it adds that mobility. It helps the lava in the magma move and it can create more explosive volcanic eruptions. More extruded materials are our pyro plastics.
We have our fire fragments, that’s what’s meant by pyro plastics. We have ash and dust which are fine glassy fragments. Pumice from frothy lava with a polite walnut-sized.
Cinders which are a little smaller than pea-sized and then particles larger than lapilli are blocks and bombs. So blocks are hardened lava, bombs are ejected as hot lava and those are generally larger than 2.5 inches.
General looks of a volcano
Some of our general features are like we have an opening at the summit which is what we call a crater Oracle, caldera. A steeple depression at the summit or a cold area is a summit depression that is greater than one kilometer in diameter.
Then there is a side vent or parasitic cone, there is a magma chamber because it’s inside the earth and then we have a pipe that is feeding all of it.
Also read: Different Magma characteristics and Volcanic eruptions
Different types of volcanoes
Cinder cones aka scoria cones.
The size ranges from ash to bombs that are just about 1 meter in size and typically these are basaltic compositions. They have very steep angles. They’re rather small. They normally occur in groups or little clusters and most form in less than one month.
So 95% form in less than one year. These form very quickly. You can see examples in Arizona and in Mexico. When we talk about size and some of the other key components of our different types of volcanoes take into consideration the amount of time it takes these to form.
Shield volcanoes
These are large domes that actually look like a shield. Primarily made up of basaltic lava. Generally large and they produce a large volume of magma or lava and most begin on the ocean floor and grow large enough to form volcanic islands.
So examples of these are the Canary Islands, Hawaiian Islands, Galapagos, Easter Island- a place in Africa and Newberry in Oregon.
Composite lava
A composite or also known as a stratovolcano. These are the most picturesque. When we think of the most are adjacent to the Pacific Ocean which is what we referred to as the Ring of Fire. These are typically large in size.
They’re symmetrical conicals created by Ash and cinders that are inner vetted with different lava flows and pyro plastics. The shape is all a function of the viscosity of lava which is typically more silica-rich and acidic.
If we have steep angles and we have lava that’s not slowing down, it’s gonna add to that. It’s gonna create deeper. These have the most violent type of activity.
They often produce new ardent and most produce lahars which are a type of volcanic mudflow. Some examples of these are the Andes in South America, the Cascades in America and Canada, and mount st.