Hawaiian lava flows are among the most visually dramatic and scientifically valuable volcanic phenomena on Earth. Each eruption creates distinct types of Hawaiian lava that shape coastlines, build new land, and reveal the inner workings of our planet.
Understanding the different types of Hawaiian lava helps visitors, residents, and researchers interpret ongoing activity and appreciate the powerful processes beneath the islands. This guide explores key characteristics, behaviors, and landforms associated with Hawaiian lava.
| Lava Type | Viscosity | Typical Flow Speed | Common Structures |
|---|---|---|---|
| Aa | High | Slow to moderate | Rough, jagged clinkers and rubble piles |
| Pahoehoe | Low to moderate | Moderate to fast | Smooth, ropy, or billowy surfaces |
| Pāhoehoe to Aa transition | 降温增稠Flow slows as temperature drops | Transitional surfaces with both smooth and rough zones | |
| Block lava | Intermediate | Moderate, channelized | Large angular blocks with rubble in between |
Characteristics of Aa Lava on Hawaii
High viscosity and brittle crust
Aa lava features higher silica content and temperature-dependent viscosity that makes it stiffer than pahoehoe. As it advances, the surface cools rapidly, forming a thick, fragmented crust of sharp, angular clinkers that often crack and tumble downhill.
Fragmented flow interior and rubble piles
Inside the crust, aa flows remain turbulent and churning, grinding rock into loose blocks. When aa lava reaches the ocean or stagnates, it builds steep, rubble-covered slopes and distinctive levees that outline once-active channels.
Hazard and accessibility
The rough, uneven surface of aa lava creates difficult hiking conditions and serious hazards for the unwary. Its ability to trip, cut, and entrap makes aa significantly more dangerous to approach than smoother pahoehoe fields.
Behavior and Landforms of Pahoehoe Lava
Low viscosity and smooth surfaces
With lower viscosity and higher temperatures, pahoehoe lava can flow more efficiently, forming sleek, ropy textures and sometimes billowy or ‘ropy’ surfaces that resemble twisted ropes frozen in motion.
Channels, tubes, and perched flows
Pahoehoe flows often develop surface channels and lava tubes that transport molten rock efficiently over long distances. These tubes can feed distant breakout sites and create perched flows that cascade over cliffs as glowing, fiery cascades.
Transition to aa and back
As pahoehoe advances and cools, it may thicken and transform into aa, especially near the flow front. Conversely, gentle slopes and efficient insulation can allow aa to re-pahoehoe, creating complex mosaics of surface types within a single field.
Formation of Block Lava in Hawaiian Settings
Intermediate viscosity with blocky texture
Block lava shares characteristics between aa and pahoehoe, forming thick lava with angular to sub-rounded blocks. Though more viscous than pahoehoe, it is typically less chaotic than classic aa due to partial melting and fragmentation during flow.
Channelized movement and marginal levees
Block lava often advances in narrow channels bordered by levees, building elevated margins as the center flows forward. These channels expose cross-sections that reveal layering and provide insights into eruption dynamics.
Preservation of flow structures and scientific value
Block lava deposits preserve clear evidence of eruption history, including gas escape patterns and flow interruptions. Scientists study these features to interpret past activity and improve hazards assessments for Hawaiian volcanoes.
Key Takeaways on Hawaiian Lava Types
- Recognize aa by its rough, clinkery surface and slow, hazardous advance.
- Identify pahoehoe by smooth, ropy textures and efficient lava tubes.
- Understand that block lava displays intermediate behavior with channelized flow.
- Monitor temperature, viscosity, and slope to anticipate flow type and behavior.
- Respect all Hawaiian lava types due to their potential for rapid landscape change and serious hazards.
FAQ
Reader questions
Why does aa lava have such a rough, jagged surface?
The high viscosity and rapid cooling of aa lava cause a thick, brittle crust to form. As the still-molten interior shifts, the brittle surface cracks and breaks into sharp, angular clinkers that create the characteristic rough, rubble-covered terrain.
How can pahoehoe lava flow so smoothly compared to aa?
Pahoehoe lava has lower viscosity and higher temperature, allowing it to maintain a thin, flexible skin that behaves like a conveyor belt of molten rock. This enables the formation of smooth, ropy surfaces and efficient lava tubes that channel flow over long distances.
What determines whether a flow becomes aa or pahoehoe?
Temperature, gas content, flow rate, and ground slope collectively control whether lava emerges as aa or pahoehoe. Faster, hotter, and more gas-rich flows tend to remain pahoehoe, while slower, cooling, or degassing flows are more likely to transform into aa.
What hazards are associated with block lava in populated areas?
Block lava can produce steep, unstable fronts and channel overflows that threaten infrastructure. Its intermediate viscosity allows it to travel considerable distances in channels, and its blocky surface increases risks for footing, vehicle movement, and rapid-onset burial during eruptions.