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.

Outlines

00:00

🌋 Lava Flow Dynamics and Formation

This paragraph discusses the characteristics and formation processes of pahoehoe and 'a'a lava flows. Pahoehoe flows are characterized by a smooth, ropey surface and are associated with slow-moving, crystal-rich lava. The viscosity of lava plays a crucial role in determining the type of flow formed; higher viscosity leads to spikier textures. Factors such as effusion rate, fountain height, and slope steepness influence shear stress, which in turn affects the lava's crust formation. The chemical composition of lava, particularly silica content, significantly impacts viscosity. Continental basaltic lava flows, which have higher silica content, tend to form spikier surfaces. The transition from pahoehoe to 'a'a crust is common as flows move down steep slopes and cool, and the fluid lava within channels can change its form continuously based on viscosity and shear stress.

05:00

🌀 Volcanic Eruptions and Lava Flow Variations

Paragraph 2 explores the progression of volcanic eruptions, focusing on how lava flows change near vents and as they move away. It explains how localized eruptions through narrow vents create high fountains, and how pahoehoe flows near vents can transition to 'a'a flows upon cooling or encountering steeper slopes. The paragraph also describes how sustained eruptions with low effusion rates form shield volcanoes, and how overflows near shields and lava lakes can produce shelly pahoehoe, a variant of lava with a thick, flexible crust. The formation of shield volcanoes like Mauna Loa is attributed to repeated eruptions of fluid lava. The paragraph also touches on more viscous basaltic lava eruptions that lead to Strombolian explosions, the formation of cinder cones, and the creation of 'a'a flows. Additionally, it discusses the formation of lava tubes, which are subterranean passages created as lava flows cool and crust over, allowing lava to travel long distances while remaining fluid.

10:08

🕳 The Lifecycle of Lava Tubes

This section delves into the formation and lifecycle of lava tubes. It begins with the initial stages of tube formation, where open channels in pahoehoe or 'a'a flows start to cool from the sides, creating a crust that gradually extends across the channel. The growth of the crust can be influenced by the speed of the lava flow, with faster flows taking longer to form a solid roof. As tubes evolve, the crust thickens, and lava can back up, leading to the formation of new surface flows that bury the tube and make the roof thicker. Over time, the lava inside the tubes thermally erodes the ground beneath, creating various cave shapes depending on the tube's activity duration. The paragraph also describes how lava tubes can collapse, form skylights, and develop multiple levels. It concludes with the discussion of the textures and formations inside lava tubes, such as stalactites, soda-straw formations, and sharkstooth textures, as well as the ecological value of cooled, collapsed lava tubes as habitats for ferns and mosses.

15:13

🌿 Post-Eruption Lava Tube Ecology

The final paragraph discusses the ecological significance of lava tubes after volcanic activity has ceased. It highlights how the intense heat within the tubes creates a variety of textures on the walls and roof, and how the release of pressure can lead to the formation of unique lava features such as soda-straw stalactites and sharkstooth textures. The paragraph also mentions how rocks can be incorporated into the lava flow, resulting in round boulders with a smooth lava coating. As eruptions end, lava drains from the tubes, leading to collapses and the eventual formation of moist, protected areas that can support plant life, even carrying water or ice. The cultural and scientific value of lava tubes is also acknowledged, as they have been important for both ancient explorers and modern scientists navigating harsh volcanic landscapes.

Keywords

💡Viscosity

Viscosity refers to the measure of a fluid's resistance to deformation at a given rate. In the context of the video, it is crucial to understanding how lava flows. The higher the viscosity, the thicker and slower the lava moves, which affects its appearance and behavior. The script mentions that 'bubble-rich toes are several times thicker than dense toes' and 'the viscosity increases greatly' as the lava cools, illustrating how viscosity changes with temperature and gas content.

💡Pahoehoe

Pahoehoe is a type of lava flow characterized by a smooth, ropey, or billowy surface. It is formed when lava flows slowly, allowing gas bubbles to stretch into long, thin shapes. The script describes 'slow-moving, crystal-rich lava tends to form spiny pahoehoe' and 'spiny pahoehoe flows a spiny texture', emphasizing the relationship between flow speed, crystal content, and surface texture.

💡A'a

A'a, also known as blocky lava, is another type of lava flow with a rough, blocky surface. It forms when lava moves faster and the crust tears due to shear stress. The script explains that 'if the lava moves faster, the crystals in the lava collide, and bind, causing the crust to tear and 'a'a to form', highlighting the role of speed and stress in lava flow types.

💡Shear Stress

Shear stress is the force that causes layers of material to slide past each other. In the script, it is mentioned as a key factor in determining whether 'a'a or pahoehoe crust forms. 'The tearing force, called shear stress, plays an important role', indicating that the type of lava crust is influenced by the internal forces within the lava flow.

💡Effusion Rate

The effusion rate is the volume of lava erupted per unit of time. It is one of the factors that influence shear stress and the type of lava formed. The script states 'the amount of lava erupted, called the effusion rate', suggesting that higher effusion rates can lead to more rapid lava flows and potentially different types of lava crust.

💡Silica Content

Silica content refers to the amount of silicon dioxide in lava, which significantly affects its viscosity. The script mentions that 'the chemical composition of lava, such as silica content, strongly affects viscosity', and that 'continental basaltic lava flows tend to have higher silica contents and higher viscosities', linking silica content to the physical properties of lava.

💡Lava Tubes

Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow. The script describes how 'hidden beneath the surface of many lava flows are long, sinuous caves called lava tubes', and explains the process of their formation, their role in insulating the lava, and how they can create caves after the lava drains.

💡Strombolian Eruptions

Strombolian eruptions are characterized by their pulsating bursts of lava and gas, often forming small, temporary cones. The script mentions 'eruptions of more viscous basaltic lava produce pulsating Strombolian explosions', indicating that the viscosity of the lava and the release of gas are key to this type of eruption.

💡Shield Volcanoes

Shield volcanoes are broad, low-profile volcanoes formed by the eruption of low-viscosity lava that spreads out easily, creating a 'shield' shape. The script refers to 'sustained eruptions with low effusion rates form gently sloping shield volcanoes', illustrating how the type of lava and the effusion rate contribute to the formation of these volcanoes.

💡Lava Spatter

Lava spatter consists of small fragments of solidified lava that are thrown into the air and land around a volcanic vent. The script describes 'small spatter cones and ridges, called spatter ramparts, build along the sides of the vents', showing how lava spatter can accumulate and form features around volcanic vents.

💡Cinder Cones

Cinder cones are steep-sided, cone-shaped volcanoes formed by the accumulation of cinders, which are small, broken pieces of solidified lava. The script mentions 'some cinder cones have a distinct horseshoe shape that is produced when cinder lands on the active lava river', highlighting the role of lava flow patterns in shaping these cones.

Highlights

The formation of spongy, bubble-rich toes in slow-moving lava flows.

Light can pass through the glassy skin of stretched tubular bubbles, giving a bronze tint.

As lava cools, its viscosity increases greatly, leading to the formation of more crystals.

The escape of many bubbles and the coalescence of remaining ones into larger bubbles.

Elongated bubbles in the interior of lava flows versus spherical ones.

Stretched and torn bubbles at the surface give a spiny texture to pahoehoe flows.

Crystal-rich lava tends to form spiny pahoehoe when moving slowly.

Faster moving lava forms 'a'a due to tearing forces from shear stress.

Shear stress plays a crucial role in determining the type of lava crust formed.

The effusion rate, fountain height, and slope steepness influence the type of lava formed.

Lava with higher silica content tends to have higher viscosity.

Spiny surfaces are more common on continental pahoehoe flows due to higher silica content.

The transition from pahoehoe to 'a'a crust as a flow moves down steep slopes and cools.

The fluid lava in channels can change continuously depending on viscosity and shear stress.

Some 'a'a flows can produce pahoehoe when they slow down on flat ground.

Basaltic eruptions often begin as fissures, leading to the formation of pahoehoe.

Eruptions from narrow vents create high fountains and 'a'a flows.

Lava tubes form when the crust of a lava flow solidifies, allowing lava to travel long distances.

Lava tubes can create branching underground caves and have various shapes.

The roof of a lava tube can collapse, creating skylights and new crust formations.

Lava tubes are valuable resources for people living in volcanic landscapes.

Transcripts

ADDING TO THE VISCOSITY OF SLOW-MOVING TOES. THE ROCK IT

FORMS CAN LOOK ALMOST SPONGY.

BUBBLE-RICH TOES ARE SEVERAL TIMES THICKER THAN DENSE TOES.

THE STRETCHED TUBULAR BUBBLES ALLOW LIGHT TO PASS THROUGH THE

GLASSY SKIN, GIVING THE SURFACE A BRONZE TINT.

AS THE FLOWS CONTINUE TO COOL, MORE CRYSTALS FORM AND THE

VISCOSITY INCREASES GREATLY. MANY OF THE BUBBLES ESCAPE AND

THE REMAINING ONES COALESCE INTO LARGER BUBBLES. BUBBLES IN

THE INTERIOR OF THESE FLOWS ARE ELONGATED INSTEAD OF SPHERICAL.

STRETCHED AND TORN BUBBLES AT THE SURFACE GIVE THESE VISCOUS

PAHOEHOE FLOWS A SPINY TEXTURE.

SLOW-MOVING, CRYSTAL-RICH LAVA TENDS TO FORM SPINY PAHOEHOE.

IF THE LAVA MOVES FASTER, THE CRYSTALS IN THE LAVA COLLIDE

AND BIND, CAUSING THE CRUST TO TEAR AND 'A'A TO FORM.

THE TEARING FORCE, CALLED SHEAR STRESS, PLAYS AN IMPORTANT ROLE

IN DETERMINING WHETHER 'A'A OR PAHOEHOE CRUST FORMS.

THE AMOUNT OF LAVA ERUPTED, CALLED THE EFFUSION RATE, THE

FOUNTAIN HEIGHT, AND SLOPE STEEPNESS ALL INFLUENCE 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. THE FASTER LAVA FLOWS

AND THE MORE IT IS TORN; THE MORE LIKELY IT IS TO FORM 'A'A.

THE CHEMICAL COMPOSITION OF LAVA, SUCH AS SILICA CONTENT,

STRONGLY AFFECTS VISCOSITY. CONTINENTAL BASALTIC LAVA FLOWS

TEND TO HAVE HIGHER SILICA CONTENTS AND HIGHER VISCOSITIES

THAN MOST HAWAIIAN LAVAS. THAT'S WHY SPINY SURFACES ARE

MORE COMMON ON CONTINENTAL PAHOEHOE FLOWS, AND WHY SOME

LAVA THAT ERUPTED ONTO FLAT GROUND PRODUCED 'A'A INSTEAD

OF PAHOEHOE.

THE CHANGE FROM PAHOEHOE CRUST TO 'A'A CRUST AS A FLOW MOVES

DOWN STEEP SLOPES AND COOLS IS WELL KNOWN. IT CAN EASILY BE

SEEN ALONG THIS SMALL FLOW, WHICH INITIALLY EMERGED AS

PAHOEHOE AND IS NOW FORMING 'A'A AT ITS FRONT.

'A'A AND PAHOEHOE FLOWS ARE DEFINED BY THEIR CRUST, WHICH

CANNOT CHANGE ONCE IT FORMS. HOWEVER, THE FLUID LAVA CARRIED

BY THE CHANNEL HAS NEITHER FORM AND CAN CHANGE CONTINUOUSLY,

DEPENDING ON VISCOSITY AND SHEAR STRESS.

SOME 'A'A FLOWS THAT SLOW DOWN WHEN THEY REACH FLAT GROUND

ACTUALLY PRODUCE PAHOEHOE FLOWS.

OTHER STAGNATED 'A'A FLOWS CAN LEAK VISCOUS, SPINY PAHOEHOE.

THIS 'A'A FLOW GRADUALLY UNDER- WENT A CHANGE TO SLABBY

PAHOEHOE AND THEN TO PAHOEHOE AS IT MOVED ONTO FLAT GROUND.

THE CRUST GROWING OVER THE CHANNEL IS KEEPING THE LAVA HOT

AND FLUID SO PAHOEHOE CAN FORM AT THE FRONT OF THE LAVA FLOW.

BASALTIC ERUPTIONS BEGIN AS FISSURES, WHICH ERUPT ENORMOUS

AMOUNTS OF LAVA. BECAUSE THE VOLUME OF LAVA IS WIDELY

DISTRIBUTED, MANY OF THE FLOWS MOVE SLOWLY AND FORM PAHOEHOE.

AS A FISSURE ERUPTION PRO- GRESSES, SMALL SPATTER CONES

AND RIDGES, CALLED SPATTER RAMPARTS, BUILD ALONG THE

SIDES OF THE VENTS.

IF THE ERUPTION LASTS WEEKS OR MONTHS, ERUPTIVE ACTIVITY WILL

LOCALIZE TO A SINGLE VENT. FORCING THE LAVA OUT THROUGH A

NARROW VENT CREATES A NOZZLE EFFECT, LIKE PUTTING A FINGER

OVER THE END OF A GARDEN HOSE. ERUPTIONS FROM NARROW VENTS

CREATE HIGH FOUNTAINS THAT CAN SPRAY LAVA UP TO 2000 FEET.

WHEN LAVA PONDS WITHIN A CONE, PAHOEHOE FLOWS TYPICALLY FORM

NEAR THE VENT. AS THEY MOVE AWAY FROM THE VENT AND COOL,

OR ENCOUNTER STEEPER SLOPES, THE PAHOEHOE FLOWS CHANGE

TO 'A'A FLOWS.

AFTER MANY HIGH FOUNTAIN EVENTS HAWAIIAN ERUPTIONS PRODUCE

LARGE CRATERLESS CONES WHEN LIGHTER MATERIAL PILES UP ON

THE DOWNWIND SIDE OF THE VENT. AT CRATERS OF THE MOON, MANY OF

THE VENTS WERE FORMED BY HAWAIIAN-STYLE FOUNTAINING AND

ARE MARKED BY LARGE ASYMMETRIC HILLS OF CINDER, WITH NO

APPARENT CRATER OR VENT.

SUSTAINED ERUPTIONS WITH LOW EFFUSION RATES FORM GENTLY

SLOPING SHIELD VOLCANOES. REPEATED OVERFLOWS OF PAHOEHOE

COAT AND RECOAT THE SURFACE OF THE SHIELDS.

OVERFLOWS CLOSE TO SHIELDS AND LAVA LAKES PRODUCE ANOTHER

VARIANT OF LAVA CALLED SHELLY PAHOEHOE. THESE FLOWS HAVE A

THICK, YET REMARKABLY FLEXIBLE, CRUST THAT DETACHES FROM THE

UNDERLYING MOLTEN LAVA AND FOLDS INTO BILLOWY FORMS WITH

HOLLOW INTERIORS.

SHELLY PAHOEHOE LAVA IS FULL OF BUBBLES AND IS MORE THAN

50% GAS BY VOLUME. GAS ESCAPING FROM THE MOLTEN INTERIOR

CREATES EVEN MORE HOLLOW SPACE BENEATH THE BUCKLED CRUST.

ON FLATTER GROUND, SHELLY PAHOEHOE CAN PILE UP INTO THICK

STACKS OF FLAT CRUSTAL PLATES.

REPEATED ERUPTIONS OF FLUID LAVA CAN BUILD ENORMOUS

SHIELD VOLCANOES. MAUNA LOA RISES 30,000 FEET ABOVE THE

SURROUNDING SEAFLOOR.

ERUPTIONS OF MORE VISCOUS BASALTIC LAVA PRODUCE PULSATING

STROMBOLIAN EXPLOSIONS. THE HIGHER VISCOSITY IS DUE EITHER

TO MAGMA COMPOSITION OR TO COOLING IN THE MAGMA CHAMBER

PRIOR TO ERUPTION. GASES CANNOT EASILY ESCAPE FROM THE STICKY

LAVA, AND ACCUMULATE UNTIL LARGE BUBBLES FORM AND

BURST FROM THE VENT.

STROMBOLIAN ERUPTIONS ARE POWERFUL AND MAKE A LOT MORE

FINE ASH THAN HAWAIIAN ERUPTIONS. THE INDIVIDUAL

BLASTS TOSS DENSE CINDER AND BOMBS WHICH ARE NOT STRONGLY

AFFECTED BY REGIONAL WIND PATTERNS.

STROMBOLIAN ERUPTIONS CONSTRUCT BEAUTIFUL CIRCULAR CONES WITH

CENTRAL CRATERS.

SOME CINDER CONES HAVE A DISTINCT HORSESHOE SHAPE THAT

IS PRODUCED WHEN CINDER LANDS ON THE ACTIVE LAVA RIVER

EXITING THE VENT AND IS SWEPT AWAY.

STROMBOLIAN ERUPTIONS STRONGLY FAVOR THE FORMATION OF 'A'A

FLOWS, LIKE THESE LARGE SHEETS OF 'A'A AROUND BANDERA CRATER.

HIDDEN BENEATH THE SURFACE OF MANY LAVA FLOWS ARE LONG

SINUOUS CAVES CALLED LAVA TUBES. WHEN THE FLOWS ARE

ACTIVE, THE TUBES ARE INCANDESCENT AND FILLED BY A

STREAM OF LAVA.

DRAINED LAVA TUBES MAKE CAVES THAT ARE OFTEN EASY TO EXPLORE

BECAUSE OF THEIR HIGH CEILINGS AND GENTLY SLOPING FLOORS.

THE FORMATION OF TUBES ALLOWS LAVA TO TRAVEL LONG DISTANCES,

WHILE REMAINING VERY FLUID. THE ROOF IS AN EXCELLENT

INSULATOR, ALLOWING LAVA TO MAINTAIN TEMPERATURES IN EXCESS

OF 2000 DEGREES FAHRENHEIT OVER MANY MILES OF TRAVEL.

LAVA TUBES COMMONLY START OUT AS OPEN CHANNELS IN EITHER

PAHOEHOE OR 'A'A FLOWS. THE CHANNELS BEGIN TO COOL FROM THE

SIDES. A THIN CRUST OF ROCK WILL GRADUALLY GROW OUT FROM

THE EDGES ACROSS THE CHANNEL, MUCH LIKE ICE ON A RIVER.

RAFTS OF CRUST CAN ALSO CLOG UP THE CENTER OF THE NARROWING

CHANNEL, HELPING TO MAKE A SOLID ROOF.

WATCH THE FLEXIBLE CRUST GROW ACROSS THE SURFACE OF A CHANNEL

IN FAST MOTION. BITS OF LAVA CATCH AND STICK TO THE EDGES

AND BOTTOM OF THE CRUST. CRUSTAL GROWTH RATES VARY

GREATLY ON DIFFERENT CHANNELS, DEPENDING ON THE SPEED OF THE

FLOW. FASTER FLOWS TEND TO TEAR UP THE CRUST AS IT FORMS, SO IT

TAKES LONGER TO GROW.

SMALLER, SLOWER FLOWS MAY DEVELOP A THICKER, BUT STILL

FLEXIBLE CRUST. IT ROLLS UP ALONG THE SIDES AND IN THE

CENTER, EVENTUALLY SOLIDIFYING INTO AN ARCH WITH A

ROPY-TEXTURED SURFACE.

EARLY ON, THE ROOF IS ONLY INCHES THICK, BUT IT CONTINUES

TO THICKEN FROM UNDERNEATH AS MORE LAVA CATCHES AND COOLS.

EVENTUALLY, THICKENING CRUST CAN CONSTRICT THE FLOW OF LAVA

BENEATH IT. THIS CAUSES LAVA TO BACK UP INSIDE AND BURST OUT IN

PLACES. THESE NEW SURFACE FLOWS THEN BURY THE REST OF THE TUBE,

MAKING THE ROOF EVEN THICKER.

AFTER A TUBE HAS BEEN SEALED OVER FOR SEVERAL WEEKS, THE

LAVA RIVER INSIDE BEGINS TO THERMALLY ERODE THE GROUND

BENEATH IT. LAVA IS SO HOT THAT THE UNDERLYING ROCK WILL SOFTEN

AND PARTIALLY MELT, ALLOWING IT TO BE SCRAPED AWAY BY THE

POWERFUL FORCE OF THE FLOWING LAVA. SMALL LEDGES ON THE WALLS

OF TUBES RECORD THE LAVA LEVELS AS EROSION PROCEEDS DOWNWARD.

THE SHAPE OF A LAVA TUBE DEPENDS ON HOW LONG IT WAS

ACTIVE. ORIGINAL CHANNELS TEND TO BE WIDE AND SHALLOW, BUT

ULTIMATELY, EROSION CARVES THEM DEEPER. TUBES THAT WERE ACTIVE

FOR ONLY A FEW DAYS TEND TO LEAVE BEHIND WIDE AND SHALLOW

CAVES, WHILE THOSE ACTIVE FOR MORE THAN A FEW WEEKS BECOME

LARGER CAVES WITH A ROUNDED PROFILE.

SOME LAVA TUBES HAVE A KEYHOLE SHAPE SHOWING BOTH THE ORIGINAL

WIDE CHANNEL AT THE TOP AND A DEEPER, NARROWER BOTTOM.

LAVA TUBE SYSTEMS VARY FRM SIMPLE TO COMPLEX. THE AMOUNT

OF INTERWEAVING IS A RESULT OF THE ORIGINAL PATHS OF THE

SURFACE FLOWS. LAVA CHANNELS MAY BE STRAIGHT, MEANDERING, OR

EVEN BRAIDED. WHILE NOT ALL OF THE CHANNELS

WILL FORM LONG-LIVED TUBES, THOSE THAT DO CAN CREATE

BRANCHING UNDERGROUND CAVES.

THE ROOF OF A LAVA TUBE CAN BECOME WEAKENED AND COLLAPSE,

FORMING A SKYLIGHT AND ALLOWING COOLER AIR INTO THE TUBE. LAVA

PASSING UNDER SKYLIGHTS COOLS AND FORMS NEW CRUST.

THICK LEDGES EMERGE FROM TUBE WALLS.

WITH TIME, AN INNER ROOF FORMS BENEATH LARGE SKYLIGHTS,

BUILDING MULTIPLE LEVELS ALONG SECTIONS OF A TUBE.

PARTIAL BLOCKAGES OF TUBES FORCE LAVA TO THE SURFACE AS

NEW FLOWS, CREATING COMPLICATED SYSTEMS OF STACKED LAVA TUBES.

THE OVERFLOWS CAN EVEN RE-ENTER THE ORIGINAL TUBE SYSTEM

FARTHER DOWNSLOPE.

INTENSE HEAT INSIDE THE TUBES CREATES A WIDE RANGE OF

TEXTURES BY MELTING THE OUTER LAYERS OF THE WALLS AND ROOF.

MOLTEN ROCK MAY FORM DRIPS FROM THE CEILING OR OOZE SLOWLY DOWN

THE WALLS. RELEASE OF PRESSURE IN THE TUBE, WHICH HAPPENS WHEN

A BLOCKED TUBE BREAKS OPEN OR DRAINS, DRIVES WATER-RICH MELT

FROM THE TUBE WALLS, EXTRUDING LITTLE BUDS.

MOLTEN LAVA FORCED FROM THE CEILING FORMS SODA-STRAW

STALACTITES. THESE HOLLOW TUBES FORM AS THE LAVA REACTS WITH

HOT AIR TO FORM A METALLIC CRUST. THE STRAW GROWS WITH

EACH DRIP OF MELT.

SPLASHING LAVA AT THE BASE OF FALLS CAN FREEZE INTO DRIPS AND

"LAVASICLES" ALONG THE WALLS.

SHARKSTOOTH TEXTURES, SEEN HERE, ARE ALSO DRIPS, LEFT

BEHIND WHEN THE LAVA LEVEL WAS HIGHER.

OTHER STALACTITES ARE FORMED BY LAVA THAT CATCHES ON WALLS OR

DRAGS ALONG PROJECTIONS FROM THE WALL OR ROOF.

ROCKS FALLING INTO THE LAVA STREAM OR BROUGHT UP DURING THE

ERUPTION MAY GET SWEPT AWAY AND ROLL AROUND IN THE LAVA. THEY

ARE OFTEN LEFT BEHIND AS ROUND BOULDERS WITH A THIN COATING

OF SMOOTH LAVA ON THE SURFACE.

WHEN AN ERUPTION ENDS, LAVA DRAINS FROM THE TUBES, WHICH

SLOWLY COOL. MANY BIG COLLAPSES IN THE TUBE SYSTEM HAPPEN

DURING THIS TIME, WITHIN JUST A FEW DAYS OF THE FLOW ENDING.

ONCE THEY ARE COOLED, COLLAPSED PARTS OF THE TUBES OFTEN MAKE

MOIST PROTECTED AREAS WHERE FERNS AND MOSSES CAN GROW.

THEY CAN CARRY WATER OR EVEN ICE YEAR AROUND.

LAVA TUBES WERE RECOGNIZED LONG AGO AS VALUABLE RESOURCES FOR

PEOPLE CROSSING, OR EVEN LIVING IN, HARSH VOLCANIC LANDSCAPES.

FROM ANCIENT EXPLORERS TO MODERN SCIENTISTS, THE INTENSE

POWER AND STRANGE BEAUTY OF ERUPTING VOLCANOES AND FLOWING

LAVA CONTINUE TO CAPTURE OUR IMAGINATION AND EXCITE OUR

SENSE OF EXPLORATION.