What are the different types of lava? Lava flows, Basaltic lava & Pahoehoe lava flows explained
Friday, 23rd August 2024
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Volcanic eruptions spread worldwide intrigue, but there’s more that meets the eye than glowing lava and global headlines.
If you want to explore different lava types, their characteristics, and how they change their landscapes, you’re in the right place!
What are Lava Flows?
A lava flow is a stream of molten rock that flows out of a volcano or volcanic vent as pressure builds during an eruption.
The glowing rivers of molten lava can travel a long way depending on the lava type, the slope of the terrain and the rate of eruption.
As the lava flows, it cools and solidifies, creating new unique landforms and altering the existing landscape. Different types of lava and lava flow can affect the landforms created.
Understanding lava flows is crucial for understanding volcanic activity and its environmental impact. Let’s dive into the different types of lava flow…
Lava Flow Types & Characteristics
There are five main types of lava flow: Pahoehoe, A’a, Blocky, and Pillow. The former three are lava flows found on land, and the latter is found underwater.
Lava flows can be classified into several types based on their characteristics:
- Basaltic Lava Flows: Are the most common type of lava flow, known for their smooth, fluid texture and dark colour. Thanks to its low silica content, basaltic lava has relatively low viscosity, allowing it to flow easily and cover large areas.Basaltic lava can form different types of lava flows including Pahoehoe lava flows, Aa lava flows, pillow lava and flood basalts. While basaltic lava flow can be slow-moving, it can still cause significant damage to infrastructure.
- Pahoehoe Lava Flows: Pahoehoe lava flow has a smooth, billowy, or ropy surface, resembling twisted braids of ropeThis type of basaltic lava has a higher temperature and a lower viscosity compared to Aa lava, allowing it to flow more fluidly and create intricate surface patterns.The name itself is a good way to remember this; the word ‘hoe’ is the Hawaiian word ‘to paddle’ (which would make swirls in the water).
- Aa Lava Flows: Contrastingly, aa lava flows are thicker and have a rough, jagged surface. Aa lava is more aggressive, making it flow more slowly and break into sharp, angular fragments as it cools.’Aa’ refers to the Hawaiian word ‘to burn’ (representing the glowing lava flow).
- Pillow Lava Flows: Pillow lava flows are formed underwater and characterised by their unique pillow-like shapes.When lava erupts beneath the ocean, the cold water causes the outer layer of the lava flow to cool rapidly. The hot lava flow inside continues and expands, creating rounded, pillow-shaped formations.Pillow lava flows can be found in mid-ocean ridges, subduction zones and lakes.
- Blocky Lava Flows: These lava flows consist of large, angular, block-like fragments, similar to Aa lava flows, but are typically larger and smoother.With a higher silica content, these lava flows are very viscous and slow-moving. They are usually associated with andesitic, dacitic, or rhyolitic lavas and are often found closer to the vent.
Each type of lava flow has distinct characteristics that influence its behaviour and the landforms it creates. Let’s dive into this…
Volcanic Landforms Created by a Lava Flow
Lava flows can create a variety of unique landforms, each with its own characteristics.
These landforms are not only fascinating geological features but also provide valuable insights into the history and behaviour of volcanic activity. Here are the landforms that are created by lava flow.
Volcanic cones
Volcanic cones are the most common types of volcanic landforms.
They are formed by the accumulation of volcanic debris around a vent. Over time, repeated eruptions can build up the cone, forming a prominent volcanic mountain. As the lava congeals, it solidifies into layers, creating a cone-shaped structure.
Each type has distinct characteristics based on the nature of the eruptions and the materials involved.
- Cinder cones- These are small, steep-sided volcanoes formed from the accumulation of volcanic fragments (cinders, ash, and scoria) ejected during relatively explosive eruptions.
- Composite (stratovolcanoes)- These are large, cone-shaped volcanoes built up from layers of lava flows, volcanic ash, and other volcanic materials.
- Lava Shields- These are broad, gently sloping volcanoes formed from fluid, basaltic lava flows that spread out over a wide area.Lava shields are formed when magma forces itself through a crack or fault in the Earth’s surface (extrusion), creating a rounded, dome-shaped structure.Lava shields are broad landforms with gentle slopes created by the accumulation of fluid lava.
Lava domes
When viscous lava mounds form on top of a vent, lava domes are formed. Because of their high viscosity, lava with high silica content often forms volcanic domes as it piles on top of a vent, rather than spreading out in a flow.
Lava Plateaus
Lava plateaus are large, flat areas of land that are formed by extensive lava flows covering a wide area and created when shield volcanoes erupt. The magma flows from the Earth’s mantle through fissures in the crust and eventually hardens into layers which build up to create the lava plateau.
Calderas
Calderas are large bowl-shaped landforms created by the collapse of the ground surface following a volcanic eruption, often when the magma chamber is emptied.
Factors that Influence Lava Flow Behaviour
Several factors can influence the behaviour of lava flows, determining how they move and the landforms they create. Some of these include:
Viscosity
The viscosity of the lava determines its flow rate and texture. The Viscosity is typically determined by the temperature and silica content of the lava, which in turn determines its flow rate and texture.
Low-viscosity lava is low in silica and flows more easily, covering larger areas.
High-viscosity lava is higher in silica and flows more slowly, usually forming thicker, more rugged structures.
Temperature
The temperature of the lava affects its viscosity and flow rate. Hotter lava is less viscous and flows more fluidly, while cooler lava is more viscous and flows more slowly.
Slope
The slope of the terrain affects the flow rate and direction of the lava. Steep slopes allow flowing lava to move more quickly, while gentler slopes slow the flow.
Eruption Rate
The rate of eruption affects the flow rate and volume of the lava. Higher eruption rates produce larger volumes of lava, which can flow more rapidly and cover greater distances.
Understanding these factors is essential for predicting the behaviour of lava flows and assessing the potential hazards they pose.
Lava Flow and Volcanic Hazards
Lava flows can pose significant hazards to people and the environment, including:
- Explosive Eruptions: Lava flows can lead to explosive eruptions, which can produce ash, gas, and rock that can affect the surrounding area. These eruptions can be highly destructive and pose serious risks to nearby communities.
- Lava Cools: As lava cools, it can solidify and create a solid surface crust. This crust can be hazardous to people and vehicles, as it can be unstable and prone to collapse. It may still be hot and molten beneath the crust of a recent lava flow.
- Pyroclastic Flows: Highly viscous lava can create unstable lava domes around the vent. When these collapse, it can trigger an explosive eruption with pyroclastic flows. These are fast-moving, hot clouds of ash, gas, and rock. These flows can travel at high speeds and reach temperatures up to 1,000 degrees Celsius, making them extremely dangerous and potentially deadly.
By understanding the hazards associated with lava flows, we can better prepare for and mitigate the risks of volcanic activity.
Examples of different types of lava flow
These eruptions show different types of lava in action.
Eyjafjallajokull 2010 Eruption, Iceland
In 2010, a largely unknown and hilariously unpronounceable volcano called Eyjafjallajökull, (ayuh-fyat-luh-yue-koutl) announced itself to the world. Although the country experiences many eruptions, few have caused such an impact across the globe as this one.
During this eruption, lava flowed from fissures, forming a lava flow of mostly a’a and pahoehoe lava.
This video shows the eruption’s effects and how Icelanders use scientific knowledge and monitoring to understand the threats of an active lava flow.
Kilauea Volcano 2010 A’a Lava Flow, Hawaii
The 2010 Kilauea Volcano eruption was a great example of a’a lava flow dynamics and how it moves through a vegetated area (that hasn’t previously experienced a lava flow).
Aa and Pahoehoe Lava
This video shows the characteristics of aa and Pahoehoe lava.
Pillow lava flow
This video shows a great example of pillow lava structures formed by underwater volcanoes in Sicily, off the coast of Pantelleria.
Comparing Lava Types Classroom Resource
Introducing the concept of volcanic chemistry and how this influences eruption behaviour to the geography classroom can be daunting.
Understanding different types of lava and characteristics will help students grasp why some volcanoes exhibit different behaviour and how this influences hazards and their management.
This resource can be used for GCSE or as an introduction for A Level students.
The ‘Comparing Lava in Iceland’ file can be downloaded as a PDF or printed and used as a classroom poster.
The suggested video links can help students visualise the different compositions of lava flows in different locations, and there are ten suggested activities that refer to the resource based on comprehension and extrapolation that will link to potential hazards and volcanic behaviour.
View the comparing lava types presentation to test your students knowledge about lava!
Comparing lava types: lesson plan
| Activity | Duration |
|---|---|
| Draw up a table to compare the two main lava types, pahoehoe and aa. How do they compare? What is similar, what is different? | 15 mins |
| Which lava type do you think creates the most explosive eruptions? Why? | 10 mins |
| Which lava type would be hardest to manage? Which would be the most dangerous? | 10 mins |
| Create a case study for two volcanic eruptions that have different lava types, for example you could compare Eyjafjallajokull and Kilauea. Include their location, the type of magma, types of lava flows, volcanic hazards during the eruption, impacts on people and the environment. | 60 mins |
| What is the link between geothermal areas and volcano location? Why are geothermal areas found where they are? | 10 mins |
| How does lava and magma type change the shape and size of a volcano? | 10 mins |
| List some of the minerals found in volcanic magma. How does mineral type change depending on the different volcanoes? | 20 mins |
| List the benefits of living near volcanoes? | 15 mins |
| Imagine you worked for the Icelandic government. How would you recommend people prepare themselves for an eruption if they lived near Eyjafjallajokull? Consider: What hazards might they be at risk of? How could they prepare their homes, vehicles, animals and farms? | 30 mins |
