Types of Basaltic Lava Flows in Hawaiian Shield Volcanoes

Hawaiian Shield volcanoes are renowned for their unique and beautiful lava flows, which are primarily composed of basalt. The two main types of basaltic lava flows that occur in these volcanic regions are pahoehoe and aa. Understanding the characteristics and formation processes of these flows is crucial for both scientific research and public safety awareness.

Introduction to Hawaiian Lavas and Shield Volcanoes

The Hawaiian Islands are part of a volcanic chain in the North Pacific Ocean. The volcanoes are classified as shield volcanoes due to their gentle slopes and broad, flat summits. These volcanoes are characterized by their high lava output and low viscosity, resulting in the formation of vast, lava-covered landscapes.

Understanding Basaltic Lava Flows

Basaltic lava is commonly found in the Hawaiian volcanoes. This type of lava is highly fluid and has a low viscosity, making it ideal for creating diverse lava flow formations. The key factors that determine the type of lava flow produced are the viscosity of the lava and the cooling rate following an eruption. These factors can significantly influence the shape and appearance of the lava flows.

Formation of Pahoehoe Lava Flows

Pahoehoe lava flows are characterized by their smooth, ropey, or stringy appearance. This type of lava is formed when the lava cools slowly, allowing the surface to form a solidified crust while the underlying lava remains fluid. As a result, the lava can flow and stretch outward, forming elongated folds like ropes or strands. The cooled surface material can then become mixed with new flows, re-crystallizing and adding to the appearance of smooth, flowing lava.

Characteristics of Aa Lava Flows

Contrarily, aa lava flows have a rugged and blocky appearance. These flows are often the result of fast-cooling, high-viscosity lava that does not form a consistent surface crust. Instead, it creates sharp, jagged fragments as the lava flows over the ground. These fragments can be thick and substantial, often stacked on top of each other, creating a rough, bumpy texture.

Factors Influencing the Type of Lava Flow

The composition and temperature of the lava are crucial in determining whether a flow will form pahoehoe or aa. Generally, flows with higher temperature and viscosity tend to produce aa, while those with lower viscosity and cooler temperatures will lead to pahoehoe. Additionally, the slope of the volcano and the rate of eruption can also influence the type of flow. Steeper slopes and faster eruptions often result in more aa flows, while flatter slopes with slower flows are more likely to produce pahoehoe.

Geological Significance of Pahoehoe and Aa Flows

The study of pahoehoe and aa flows provides valuable insights into volcanic processes and the evolution of the land. The patterns and textures of these flows can offer clues about the historical and current activity of the volcano. For instance, studying the thickness and composition of pahoehoe flows can help geologists understand the past eruptions' intensity and duration, while analyzing aa flows can reveal information about the eruption's speed and style.

Public Safety and Environmental Impact

Understanding the characteristics of pahoehoe and aa flows is also essential for public safety, as these flows can pose significant risks during volcanic eruptions. For example, the high viscosity of aa flows can make them more dangerous and slower to move, while pahoehoe flows are generally faster and smoother, making them slightly less hazardous. Knowing which type of flow to expect can help in developing effective evacuation plans and warning systems.

Conclusion

The natural beauty and scientific importance of pahoehoe and aa lava flows are evident in the Hawaiian Shield volcanoes. By studying these flows, scientists can gain a deeper understanding of the processes that shape our planet. Moreover, the knowledge of these different lava flow types is crucial for ensuring the safety of residents and visitors in volcanic regions.

References

For a more detailed study, refer to the following resources:

USGS Volcano Hazards Program Hawaii Volcanoes National Park Lava Flow Ergodicity Manual