Hi, my name is Ruby. With my Miller Fellowship, I want to understand how does lava flows. So, first of all, what is lava? Lava is the hot molten rock generated by geothermal energy expelled from Earth’s surface during an active eruption.
Volcanic eruptions are some of the most spectacular events on earth and the context of everyday lives. The most voluminous volcanic activity on our planet occurs on the ocean’s bottom, at the so-called mid-ocean ridges. These are the edges of plates that are pulling apart. In these settings, molten material is rising from deep inside the earth and erupting on the surface.
The most important place where this happens on our planet is the mid-ocean ridges. This ring of mountain ranges winds for about 60,000 kilometers, like the seams of a baseball around our planet.
What is lava flow?
Lava is the second kind of material that comes out of volcanoes. It comes out the edges of large volcanic structures and piles up with the pyroclastic material to make large volcanic cones. But it also leaks out of giant cracks or fissures in the seafloor and other places. It just sorts of oozes out and pours across the surface of the earth as it cools.
In its original state, lava flows very much like a very thick fluid, a kind of honey. Lava flow creates different types of lava tubes. However, once the lava’s exposed to air, it could also cool into solid rocks. So the fact that lava can transition from the fluid into a solid makes its flow quite complicated.
The place where the lavas are coming out is extremely narrow, just a kilometer or so wide. The lava is generated as the Earth’s lithosphere plates are pulled apart, material rises beneath it to fill that widening gap.
And as it rises, the material begins to melt. Because the melt is much less dense than the surrounding rock, it rises very rapidly to the surface, sort of like how a hot air balloon rises to the top of a room.
It beats the solid material that’s also moving upward to the surface. Much of that material will solidify before it reaches the surface because it begins to feel the cool, outer surface of the earth as it rises. But some of it will leak out onto the surface as lava.
I’m interested in understanding a specific type of lava flow called Pahoehoe. This type of flow occurs when the lava’s top surface cools to form a skinny solid crust, and this crust can inflate and stretch like a balloon, but it can also rupture like an eggshell.
And this type of flow is often challenging to predict. One of the main reasons for that is that the old lava flow that has already occurred has created a solid surface that changes the terrain over which newer lava would flow.
Also, this kind of flow can travel for long distances and long periods. For that reason, the lava flow has and is actively changing our planet’s landscapes, which may also be true for Mars and Venus, where lava flow has been observed.
A better understanding of this flow can help us gain better insights into planetary surfaces’ evolution histories. In the United States, the best place to look for active lava flow would be in Hawaii. And, just earlier this year in 2018, there was an active event that lasted for months. Also, lava flow can be very devastating to human lives.
It can devour public infrastructures such as roads and buildings. It can take away your home. Another motivation to study lava flow would be to develop better predictive models to inform decision-makers and residents about when and where we need to evacuate.
Most of that volcanic activity makes basaltic lava. Lava comes in many different compositions, and those compositions vary mainly because of the amount of silica in the lava. More silica makes the lava more viscous, like Blocky lava. Also, Less silica makes it runnier or has a lower viscosity.
The low viscosity lava that flows in streams most commonly is called basalt. It’s black lava, and it’s very common. It’s erupted on the bottom of the ocean and in places like Hawaii and Iceland. One type that forms by the explosion and the blowing apart of molten material near volcanic centers is pyroclastic.
It mostly piles up close to volcanoes. But in the most violent eruptions, the material is also blown into the stratosphere. Both volcanic material, particles, volcanic ash, and gases are blown into the atmosphere. They can change our climate in the short term or even in the long term.
Lava pours out, and it takes on many different shapes. One of the typical shapes is called pillow lavas, and as the name suggests, it’s a sort of rounded, bulbous blobs that are usually about a meter across or about the size of your pillow.
And they pile up in this sort of lumpy pile, and most of the lava on the seafloor has that form. Other lavas on the seafloor come out in very smooth-looking sheets that can be more than a mile long.
Types of lava flow
There are two types of lava flows.
1. Mafic or basaltic lava flows: Basaltic or mafic lava means lower viscosity which means it is more likely to flow readily. Basalt melts at an extremely high temperature because it contains more of those mafic minerals like olivine and pyroxene with extremely high melting temperatures. It means that it takes more temperature to melt them.
So mafic lavas will be extremely hot. They will obviously have a lower silica content, and they will also have a lower viscosity. These mafic lavas will tend to be thin and fluid-like, and they can flow for very long distances.
2. Felsic or rhyolitic lava flows: These tend to be cooler lavas because felsic lavas containing felsic minerals like quartz and potassium feldspars have minerals that will begin to melt at cooler temperatures. So the lava will tend to be cooler than something like mafic lava.
They are very high in silica content which means that they will be extremely viscous. Felsic lavas tend to be thin and sticky lava flows where they don’t really flow at all for the most part. It flows nicely out of the volcanic vent. It’s going to blow its way out and be extremely explosive, essentially.
Lava flow example: The dark spots on the moon are called the lunar mare. Mars is another place where there are extensive lava flows. If you look at the Pathfinder missions, the current rover missions to Mars, you’ll be able to see lots of lava there. The biggest volcano in the solar system, Olympus Mons, 600 kilometers across at the base and 25 kilometers high, is an extensive volcanic feature.
Lava flow effects
Lava plays an important role in the early history of almost all planets, certainly in all the planets of our solar system. Planets are first formed from dust clouds that collapse upon one another, crushed together by gravity, and then pounded by various meteor impacts. Together with radiogenic heat, the plant starts very hot and then slowly cools through time.
The Earth, probably about four and a half billion years ago, probably had large magma oceans or lava oceans all over its surface soon after it formed.
In fact, there’s ongoing volcanic activity elsewhere in our solar system, for example, on the moons of Jupiter. Io, in particular, is the most active volcanic center in our solar system as a whole. So lava plays a fundamental role in the way planets develop, and it’s a fundamental building block in building new planetary real estate.
Philpotts, Anthony R.; Ague, Jay. Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press.
Bonnichsen, B.; Kauffman, D.F. “Physical features of rhyolite lava flows in the Snake River Plain volcanic province, southwestern Idaho.” Geological Society of America Special Paper. Geological Society of America Special Papers.