Imagine standing at the edge of creation, where the Earth reshapes itself with fire and stone. Lava flow, the molten heartbeat of our planet, is both a destroyer and a creator, carving paths of devastation and laying the foundations for new lands. This primal force, emerging from the depths of the Earth, is a vivid reminder of the planet’s dynamic nature. But what exactly is a lava flow, and how does this fiery river sculpt the surface of the Earth?
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 are part of the context of everyday life. Our planet’s most voluminous volcanic activity occurs on the ocean’s bottom, at the mid-ocean ridges. These are the edges of plates that are pulling apart. In these settings, molten material rises deep inside the earth and erupts on the surface.
The mid-ocean ridges are the most important places where this happens on our planet. This ring of mountain ranges winds for about 60,000 kilometers, like the seams of a baseball around our planet.
In this post, we’ll journey to the heart of volcanoes, exploring the origins, types, and impacts of lava flows. From the slow-moving basaltic rivers to the explosive andesitic streams, join us as we unravel the mysteries of lava flow, discovering the power and beauty of this unstoppable force of nature.
What Is Lava Flow?
Lava is the second type of material that comes out of volcanoes. It comes from the edges of large volcanic structures and piles up with pyroclastic material to make large volcanic cones. But it also leaks out of giant cracks or fissures in the seafloor and other places. It oozes out and pours across the earth’s surface as it cools.
In its original state, lava flows like a very thick fluid, a type of honey. Lava flow creates different types of lava tubes. However, once the lava is exposed to air, it can cool into solid rocks. So, the fact that lava can transition from fluid into a solid makes its flow quite complicated. Here are some key characteristics of lava flows:
Viscosity: The viscosity of lava determines its flow characteristics. Lava viscosity depends on temperature, chemical composition, and gas content. High-viscosity lava is thicker and more resistant to flow, often resulting in slow-moving, thick lava flows. In contrast, low-viscosity lava flows more easily and can travel longer distances.
Types of Lava: Different types of lava flows are based on their composition and viscosity. The two main types are:
Aa Flows: Aa flows are characterized by rough and jagged surfaces. They have higher viscosity and tend to move slowly, causing the solid crust to break and form rough, blocky terrain.
Pahoehoe Flows: Pahoehoe flows have smooth and ropy surfaces. They are associated with lower viscosity and can move more fluid, resulting in undulating rope-like features.
Temperature: Lava can reach extremely high temperatures, typically ranging from 700 to 1,200 degrees Celsius (1,292 to 2,192 degrees Fahrenheit). The exact temperature depends on the composition of the lava and its eruption source.
Speed: The speed of lava flows can vary significantly. Some lava flows may move slowly at a few meters per hour, while others can advance at several kilometers per hour. The speed of lava flow depends on factors such as viscosity, slope, volume, and eruption dynamics.
Channelized Flows: Lava flows often follow pre-existing pathways or channels, especially in hilly or mountainous terrain. These channels provide a route for the lava to flow, concentrating the flow and directing it downhill.
Surface Crusting: As lava flows, the outer layer of the flow can solidify and form a solid crust. This crust insulates the still-molten lava beneath, allowing it to continue flowing. The crust can crack, break, or be pushed upward as the lava beneath continues to move.
Volcanic Gases: Lava contains various gases, including water vapor, carbon dioxide, sulfur dioxide, etc. These gases can be released from the lava flow, leading to volcanic gas emissions and potentially affecting air quality and the environment.
The lavas coming out are extremely narrow, a kilometer or so wide. The lava is generated as the Earth’s lithosphere plates are pulled apart, and material rises beneath it to fill that widening gap. As it rises, the material begins to melt. Because the melt is much less dense than the surrounding rock, it rises rapidly to the surface, like 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 flow occurs when the lava’s top surface cools to form a solid, skinny crust. This crust can inflate and stretch like a balloon but also rupture like an eggshell.
This type of flow is often challenging to predict. One of the main reasons 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 flow can travel for long distances and long periods. For that reason, the lava flow is actively changing our planet’s landscapes, which may also be true for Mars and Venus, where lava flow has been observed.
Understanding this flow can help us understand the evolution histories of planetary surfaces. Hawaii is the best place in the United States to look for active lava flow. Earlier this year, in 2018, an active event lasted for months. Also, lava flow can be very devastating to human lives.
It can devour public infrastructures such as roads and buildings. Moreover, 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, 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 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 the material is also blown into the stratosphere in the most violent eruptions. Volcanic material, particles, volcanic ash, and gases are blown into the atmosphere. They can change our climate in the short or even 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, they’re rounded, bulbous blobs that are usually about a meter across or about the size of your pillow. They pile up in this 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 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 have a lower silica content, and they will also have a lower viscosity. These mafic lavas tend to be thin and fluid-like and can flow 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 will be extremely viscous. Felsic lavas tend to be thin and sticky lava flows where they don’t 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.
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 and 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 the base and 25 kilometers high, is an extensive volcanic feature.
Lava Flow Effects
Lava is important in the early history of almost all planets, certainly in our solar system’s planets. Planets are formed from dust clouds that collapse, are crushed together by gravity, and then pounded by various meteor impacts. The plant starts hot with radiogenic heat and then slowly cools over time. The Earth, probably about four and a half billion years ago, had large magma or lava oceans all over its surface soon after it formed.
There’s ongoing volcanic activity elsewhere in our solar system, for example, on the moons of Jupiter. Io, in particular, is our solar system’s most active volcanic center. So lava plays a fundamental role in how planets develop, and it’s a fundamental building block in building new planetary real estate.
Understanding lava flows allows us to appreciate not only the spectacle of a volcano but also the intricate processes that drive our planet’s continual rebirth. These rivers of molten rock are a testament to Earth’s ever-changing face, a reminder of the potent forces that lie just beneath our feet.
May this journey through the world of lava flows inspire a deeper respect for the natural forces that shape our world and a curiosity to explore the other wonders that our planet holds. So, the next time you see a volcanic eruption, either in person or through the screen, remember the incredible journey of lava from the Earth’s fiery heart to its surface, a journey of destruction, creation, and transformation.
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.