Magma That Erupts Onto Earth's Surface Is Called

Magma That Erupts Onto Earth's Surface Is Called Lava: A Comprehensive Guide

Magma, the molten rock found beneath the Earth's surface, is a fascinating and powerful force of nature. When this molten rock makes its way to the surface, it undergoes a dramatic transformation, becoming what we know as lava. Understanding the differences between magma and lava, and the various types of lava flows, is crucial to comprehending volcanic activity and its impact on our planet. This comprehensive guide delves into the specifics of lava, exploring its formation, characteristics, and the diverse geological formations it creates.

From Magma to Lava: The Journey of Molten Rock

The term "magma" refers to the molten rock found beneath the Earth's surface, typically within the Earth's mantle and crust. This molten rock is a complex mixture of silicate minerals, dissolved gases, and crystals. The pressure exerted by overlying rock layers keeps magma contained. However, when this pressure is overcome—often due to tectonic plate movements, changes in pressure, or the buildup of gases—magma ascends towards the surface.

As magma rises, the pressure surrounding it decreases significantly. This decompression allows dissolved gases within the magma to expand rapidly, much like shaking a soda bottle. This expansion creates immense pressure, further propelling the magma upwards. The decrease in pressure also leads to the outgassing of volatile compounds, changing the magma's composition.

Finally, when magma breaches the Earth's surface, it undergoes its final transformation and is then officially designated as lava. This transition is marked by a significant change in temperature, pressure, and gas content. The loss of dissolved gases changes its viscosity and flow properties drastically.

Types of Lava: A Diverse Spectrum of Molten Rock

Lava isn't a monolithic substance; it displays a significant degree of variation depending on its chemical composition, temperature, and gas content. This diversity leads to different types of lava flows and volcanic landforms. Here are some key types:

1. Pahoehoe Lava: The Smooth, Ropey Flow

Pahoehoe (pronounced pah-HOY-hoy), also known as "ropy lava," is characterized by its smooth, billowing, and often wrinkled surface. This type of lava has a relatively low viscosity, meaning it flows relatively easily. The smooth surface is formed as the lava's outer layer cools and solidifies while the still-molten interior continues to flow beneath. Pahoehoe flows are often associated with relatively low silica content and high temperatures. They can travel considerable distances, often forming lava tubes—subterranean channels that insulate the molten rock, allowing it to flow for long periods and great distances.

2. ʻAʻā Lava: The Rough, Jagged Flow

In contrast to pahoehoe, ʻaʻā (ah-ah) lava is characterized by its rough, blocky, and fragmented surface. This type of lava has a higher viscosity than pahoehoe, making it flow more slowly and clumsily. As it flows, the outer layer cools and solidifies, breaking apart into sharp, jagged pieces that are carried along on the still-molten interior. The resulting flow is characterized by a chaotic and uneven surface. ʻAʻā flows are often associated with higher silica content and slightly lower temperatures than pahoehoe.

3. Pillow Lava: Underwater Eruptions

Pillow lava is a type of lava formed during underwater volcanic eruptions. As the hot lava emerges from a vent, it instantly cools and solidifies upon contact with the cold water, forming distinctive pillow-like shapes. These pillow-shaped structures are often stacked on top of each other, creating a unique and readily identifiable geological formation. The rapid cooling process causes the formation of a glassy crust on the outer surface of each pillow. Pillow lavas are common along mid-ocean ridges, where submarine volcanism is prevalent.

4. Block Lava: Viscous and Slow-Moving

Block lava is characterized by its highly viscous nature, resulting in slow-moving flows. This type of lava has a higher silica content and a lower temperature than pahoehoe or ʻaʻā. As it cools, it forms large, angular blocks that pile up on top of each other. Block lava flows are typically shorter and thicker than other types of lava flows and often have a relatively steep slope.

5. Pyroclastic Flows: A Deadly Combination

While not strictly lava in the traditional sense, pyroclastic flows are a crucial aspect of volcanic activity and often associated with lava eruptions. These flows are a mixture of hot gases, volcanic ash, and fragmented lava. They are extremely fast-moving and incredibly destructive, posing a significant hazard to human life and infrastructure. Pyroclastic flows can travel at speeds exceeding 100 kilometers per hour and reach temperatures exceeding 700° Celsius. They can flatten entire forests and bury towns under thick layers of ash and debris.

The Composition and Properties of Lava

The properties of lava, such as its viscosity and flow behavior, are primarily determined by its chemical composition, specifically its silica content. Lava with a higher silica content is more viscous, meaning it flows more slowly and tends to form steeper-sloped flows. Lava with a lower silica content is less viscous and flows more readily. Temperature also plays a significant role, with hotter lavas being less viscous. The presence of dissolved gases also influences lava's fluidity and eruptive behavior.

The Geological Impact of Lava Flows

Lava flows have a profound impact on the Earth's geology, shaping landscapes and creating diverse geological formations. The solidification of lava forms igneous rocks, which are a major component of the Earth's crust. Over time, erosion and weathering processes can sculpt these rocks into impressive landforms, including:

• Lava plateaus: Extensive areas covered by successive lava flows.
• Volcanic cones: Cone-shaped formations built up by the accumulation of lava flows.
• Lava tubes: Subterranean channels formed by the cooling and solidification of lava flows.
• Lava domes: Dome-shaped structures formed by the slow extrusion of viscous lava.
• Pillow lava fields: Underwater formations built up by the accumulation of pillow lava.

Studying Lava: Unveiling Earth's Secrets

The study of lava is crucial for understanding volcanic processes and mitigating the risks associated with volcanic eruptions. Scientists use a variety of methods to study lava, including:

• Direct observation: Observing active lava flows during eruptions.
• Geochemical analysis: Analyzing the chemical composition of lava samples.
• Petrological analysis: Studying the texture and mineral composition of solidified lava.
• Geophysical techniques: Using seismic and other geophysical methods to monitor magma movement beneath the Earth's surface.
• Remote sensing: Using satellite and aerial imagery to monitor volcanic activity and lava flows.

Conclusion: The Ever-Evolving Landscape of Lava

Lava, the molten rock that emerges from the Earth's interior, is a powerful force of nature that shapes landscapes, creates diverse geological formations, and plays a crucial role in the Earth's dynamic processes. Understanding the various types of lava, their properties, and their geological impact is essential for comprehending volcanic activity and mitigating the risks associated with these powerful events. Ongoing research continues to unveil the complex processes involved in the formation and behavior of lava, deepening our knowledge of the Earth's dynamic and ever-changing systems. From the smooth, ropy flows of pahoehoe to the destructive fury of pyroclastic flows, lava’s diverse nature continues to fascinate and challenge scientists and onlookers alike. The study of lava offers a glimpse into the powerful forces shaping our planet and provides crucial insights into the processes that have shaped the Earth we inhabit today.