Lava Flows and Lava Tubes - Part 2

Summary

This script explores the fascinating world of lava flows, detailing how viscosity affects their appearance as pahoehoe or 'a'a. It explains how factors like shear stress, effusion rate, and chemical composition determine the type of lava crust formed. The script also delves into the formation of shield volcanoes, the creation and exploration of lava tubes, and the various textures and structures formed by lava, capturing the imagination with the dynamic nature of volcanic activity.

Takeaways

• 🌋 The viscosity of lava affects its movement and the type of surface it forms, with slower lava creating spongy, bubble-rich surfaces.
• 🌌 The stretched tubular bubbles in slow-moving lava allow light to pass through, giving the surface a bronze tint.
• 💧 As lava cools, its viscosity increases, leading to the formation of more crystals and the escape or coalescence of bubbles.
• 🔍 The shape of bubbles in lava flows can indicate the movement speed, with elongated bubbles in slower flows and spherical ones in faster ones.
• 🏔️ Spiny pahoehoe forms from slow-moving, crystal-rich lava, while faster-moving lava forms 'a'a due to shear stress and tearing of the crust.
• 📊 The effusion rate, fountain height, and slope steepness are key factors influencing the type of lava crust formed.
• 🌐 The chemical composition of lava, particularly silica content, affects its viscosity, with higher silica leading to higher viscosity.
• 🛤️ Changes in lava crust from pahoehoe to 'a'a can occur as a flow moves down steep slopes and cools.
• 🌀 Lava tubes form when the crust of a lava flow hardens and insulates the molten lava beneath, allowing it to travel long distances.
• 🗻 The type of volcano formed depends on the viscosity of the lava and the eruption style, with shield volcanoes formed by fluid lava and cinder cones by more viscous lava.

Q & A

What causes the spongy appearance in lava flows?

The spongy appearance in lava flows is caused by the formation of stretched tubular bubbles, which are several times thicker than dense toes, allowing light to pass through the glassy skin and giving the surface a bronze tint.

How do the bubbles in the interior of lava flows differ from those on the surface?

Bubbles in the interior of lava flows are elongated instead of spherical, whereas stretched and torn bubbles at the surface give the viscous pahoehoe flows a spiny texture.

What is the role of shear stress in determining the type of lava crust formed?

Shear stress plays an important role in determining whether 'a'a or pahoehoe crust forms. The faster the lava flows and the more it is torn, the more likely it is to form 'a'a.

How does the effusion rate of lava influence the type of lava formed?

The amount of lava erupted, called the effusion rate, influences the shear stress and type of lava formed. Lava moving rapidly down a steep slope or in a wide channel is stressed much more than lava moving slowly on flat ground.

Why are spiny surfaces more common on continental pahoehoe flows?

Spiny surfaces are more common on continental pahoehoe flows because continental basaltic lava flows tend to have higher silica contents and higher viscosities than most Hawaiian lavas.

How can 'a'a flows produce pahoehoe flows when they slow down on flat ground?

'A'a flows can produce pahoehoe flows when they slow down on flat ground because the crust growing over the channel keeps the lava hot and fluid, allowing pahoehoe to form at the front of the lava flow.

What is the difference between shelly pahoehoe and regular pahoehoe?

Shelly pahoehoe has a thick yet remarkably flexible crust that detaches from the underlying molten lava and folds into billowy forms with hollow interiors, while regular pahoehoe has a more solid crust.

How do lava tubes form and what is their significance?

Lava tubes form as the crust of a lava flow cools and solidifies from the sides, creating a roof over the flowing lava. They allow lava to travel long distances while remaining very fluid, and their roofs act as excellent insulators.

What factors contribute to the complexity of lava tube systems?

The complexity of lava tube systems is contributed by the original paths of the surface flows, which can be straight, meandering, or braided. The amount of interweaving is a result of these paths.

How do lava tubes contribute to the formation of shield volcanoes?

Repeated eruptions of fluid lava can build enormous shield volcanoes. Overflows of pahoehoe coat and recoat the surface of the shields, contributing to their formation.

What are some of the unique features found inside lava tubes?

Lava tubes can have features such as soda-straw stalactites, sharktooth textures, and thick ledges that form from tube walls. They can also have multiple levels and complex systems of stacked tubes.