What is Lava? A Molten Revelation
Lava is molten rock that has erupted onto the Earth’s surface (or the surface of another planet or moon). This extrusive igneous rock, distinguished from magma (molten rock beneath the surface), solidifies upon cooling, forming various volcanic rock formations.
The Essence of Eruption: Understanding Lava’s Composition and Behavior
Lava’s journey from the Earth’s interior to the surface is a dramatic testament to the planet’s dynamic nature. It’s not just “hot rock”; its specific properties, including temperature, viscosity, and composition, determine its behavior and the types of volcanic landforms it creates.
Compositional Variety: From Basalt to Rhyolite
Lava is primarily composed of silicate minerals, but its exact composition varies depending on the source magma. The most common type of lava is basaltic lava, characterized by its low silica content (around 50%) and high iron and magnesium. This composition gives it a dark color and relatively low viscosity, allowing it to flow easily.
At the other end of the spectrum is rhyolitic lava, which is rich in silica (over 70%). This high silica content makes it incredibly viscous and slow-moving, often forming steep-sided lava domes rather than flowing rivers. Other types of lava include andesitic and dacitic, falling between basaltic and rhyolitic in composition and properties.
Temperature and Viscosity: The Flow of Fire
The temperature of lava ranges from approximately 700°C (1300°F) to 1200°C (2200°F), with basaltic lavas typically being hotter. Viscosity, a measure of a fluid’s resistance to flow, is a crucial factor influencing lava behavior. As mentioned, high-silica lavas like rhyolite are highly viscous, while low-silica lavas like basalt are more fluid. Temperature also affects viscosity; hotter lavas generally flow more easily. The presence of dissolved gases also contributes to viscosity; the more gas, the less viscous the lava.
Effusive vs. Explosive Eruptions: A Matter of Gas
The style of a volcanic eruption – effusive or explosive – is largely determined by the lava’s viscosity and gas content. Low-viscosity basaltic lavas tend to produce effusive eruptions, characterized by the relatively gentle outflow of lava. This lava can form lava flows, lava channels, and lava tubes. Conversely, highly viscous, gas-rich lavas are prone to explosive eruptions, where the buildup of pressure from dissolved gases leads to violent explosions of ash, rock, and lava fragments.
Lava Flows and Landforms: Sculpting the Landscape
The solidification of lava creates a diverse range of volcanic landforms, each reflecting the lava’s properties and eruption style.
Pahoehoe and A’a: Two Faces of Basaltic Lava
Basaltic lava flows can take on two distinct forms: pahoehoe and a’a. Pahoehoe is characterized by its smooth, ropy surface, formed as the lava cools and wrinkles as it flows. A’a, on the other hand, has a rough, jagged, and spiny surface, resulting from the lava’s higher viscosity and faster cooling rate. The same lava can transition from pahoehoe to a’a as it loses heat and becomes more viscous.
Lava Tubes and Channels: Underground Rivers of Fire
Lava tubes are tunnel-like conduits formed when the surface of a lava flow cools and solidifies, while the molten lava continues to flow beneath. These tubes allow lava to travel long distances without losing heat, contributing to the formation of extensive lava fields. Lava channels are open, river-like pathways that carry molten lava across the landscape.
Volcanic Cones and Plateaus: Structures Built by Eruption
The accumulation of lava and volcanic debris over time can create various volcanic structures. Shield volcanoes, characterized by their broad, gently sloping shapes, are formed by the accumulation of fluid basaltic lava flows. Cinder cones are steep-sided cones formed by the accumulation of volcanic ash and cinders ejected during explosive eruptions. Stratovolcanoes (also known as composite volcanoes) are large, conical volcanoes built up of alternating layers of lava flows, ash, and other volcanic debris, representing a complex history of both effusive and explosive eruptions. Extensive lava plateaus are formed by the accumulation of vast quantities of basaltic lava over long periods, often resulting from fissure eruptions.
FAQs: Unveiling the Mysteries of Lava
Here are some frequently asked questions about lava, designed to clarify common misconceptions and provide deeper insights:
FAQ 1: Is lava the same as magma?
No, lava and magma are not the same. Magma is molten rock located beneath the Earth’s surface, while lava is magma that has erupted onto the surface. The term changes based on its location relative to the earth’s crust.
FAQ 2: What determines the color of lava?
The color of lava is primarily determined by its temperature and composition. Hotter lavas tend to glow with a brighter, more orange or yellow hue, while cooler lavas appear darker red or even black. The chemical composition, particularly the iron content, also affects the color.
FAQ 3: How fast does lava flow?
The speed of lava flow varies greatly depending on its viscosity, slope, and volume. Highly fluid basaltic lavas can flow at speeds of several meters per second, while viscous rhyolitic lavas may move only a few centimeters per hour. Some extremely fast-moving lava flows have reached speeds of over 40 mph.
FAQ 4: Can you walk on cooled lava?
Yes, but it depends on the type of cooled lava. Pahoehoe flows, with their relatively smooth surfaces, can be walked on with caution. A’a flows, with their jagged and unstable surfaces, are much more difficult and dangerous to traverse. Regardless, always wear appropriate footwear and be aware of the risk of sharp edges and unstable rocks.
FAQ 5: What is the danger of lava?
Lava poses several dangers. The extreme heat can cause severe burns and ignite flammable materials. Lava flows can destroy structures and disrupt infrastructure. Volcanic gases released by lava, such as sulfur dioxide, can be toxic and cause respiratory problems. Volcanic ash can also cause respiratory problems, damage machinery, and disrupt air travel.
FAQ 6: How long does it take for lava to cool?
The cooling rate of lava depends on several factors, including its volume, surface area, and the surrounding environment. Thin lava flows can cool within hours or days, while thick flows or lava lakes may take months or even years to completely solidify.
FAQ 7: What is obsidian?
Obsidian is a volcanic glass formed when lava cools very rapidly, preventing the formation of crystals. It is typically black or dark-colored and has a smooth, glassy texture. Obsidian is often used for making tools, jewelry, and decorative objects.
FAQ 8: Can lava be used for anything?
Yes, cooled lava rock has several uses. It can be used as a building material, for landscaping, and as a source of minerals. In some areas, geothermal energy extracted from volcanic regions is used to generate electricity.
FAQ 9: What gases are released by lava?
Lava releases a variety of gases, including water vapor, carbon dioxide, sulfur dioxide, hydrogen sulfide, and hydrochloric acid. These gases can pose a health hazard and contribute to air pollution. Sulfur dioxide, in particular, can react with water in the atmosphere to form acid rain.
FAQ 10: How do scientists study lava?
Scientists use a variety of methods to study lava, including remote sensing techniques, such as satellite imagery and thermal infrared imaging, to monitor lava flows and temperatures. They also collect lava samples for laboratory analysis to determine their chemical composition and physical properties. In some cases, scientists venture close to active lava flows to make direct observations and measurements, using heat-resistant suits and equipment.
FAQ 11: What is a lava bomb?
A lava bomb is a blob of molten lava ejected from a volcano during an eruption. Lava bombs can range in size from a few centimeters to several meters in diameter and can travel long distances from the vent. They pose a significant hazard due to their high temperature and impact force.
FAQ 12: Where can I see lava flows?
Active volcanoes with frequent effusive eruptions, such as those in Hawaii, Iceland, and Italy (Mount Etna), offer opportunities to witness lava flows. However, it is crucial to visit these sites with experienced guides and follow safety precautions to minimize the risk of injury. Always check local alerts and warnings before visiting any volcanic area.