Pillow lava is a type of volcanic rock that forms when lava erupts under water and rapidly cools, creating rounded, pillow-shaped structures. The cooling lava creates a distinctive texture and shape, similar to a stack of pillows or a bunch of balloons, which is how this geological feature got its name. This type of lava is primarily found on the ocean floor but can also occur in deep lakes or other subaqueous environments.
Understanding Pillow Lava Formation
Lava, the molten rock expelled by a volcano, comes in a variety of types and forms different geological features depending on the conditions under which it solidifies. Pillow lava is unique in that it forms specifically in the presence of water.
Conditions for Pillow Lava Development
For pillow lava to develop, two main conditions must be met:
1. The eruption must take place underwater.
2. The water must be deep enough to exert significant pressure on the erupting lava.
When lava comes into direct contact with water, it cools much more rapidly than it would in air. The difference in temperature between the hot lava and the surrounding water causes the outer layer of lava to solidify almost instantly. This results in the formation of a thin, glassy crust around the still-molten interior of the lava flow. As more lava continues to push through from beneath, the pressure causes the crust to fracture, creating an opening through which the molten material can escape. New layers of solidified lava build up around the opening, forming a bulbous structure that resembles a pillow.
Growth and Characteristics of Pillow Lava
The size and shape of pillow lava can vary greatly. Individual pillows can be anywhere from a few centimeters to several meters in diameter. Characteristics of pillow lava include:
– The glassy skin or crust, which is formed due to rapid cooling.
– A fine-grained internal structure because of the quick cooling rate.
– Radial jointing patterns from contraction as the pillows cool and solidify.
– A tubular or elongated shape as the lava is extruded.
– Interconnected lobes that stack upon one another, often in a chaotic manner.
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The Significance of Studying Pillow Lava
Pillow lava provides vital clues to geologists about the earth’s underwater and geologic processes.
Insights into Underwater Volcanic Activity
Much of Earth’s volcanic activity is submarine, and pillow lava is a direct record of these underwater eruptions. By studying pillow lavas, scientists can gain insights into the dynamics of undersea volcanic activity—the temperatures and pressures involved, the rapidity of the eruptions, and the composition of the erupting lava. All these factors tell scientists about the nature of the mantle beneath the ocean floor.
Uncovering Past Environments
Pillow lavas not only form on contemporary ocean floors. They are found within the geological record stretching back billions of years. When geologists encounter pillow lavas on land within ancient rock sequences, it’s an indication that those rocks were originally formed underwater. This information helps to reconstruct past environments and the geological history of the Earth.
Contribution to Ocean Floor Mapping
Mapping the distribution of pillow lavas helps scientists understand the structure of the ocean floor. These formations often indicate the presence of mid-ocean ridges and other tectonic features that are important to the study of plate tectonics.
Where Can Pillow Lava Be Found?
Pillow lava is most commonly associated with mid-ocean ridges—underwater mountain ranges where tectonic plates are spreading apart and new oceanic crust is being formed. However, these forms can also be found in other submarine volcanic contexts, such as:
– Subaqueous parts of seamounts or oceanic volcanoes.
– Coastal submarine environments where lava flows into the sea.
– In deep freshwater environments such as subglacial lakes or deep ancient lakes preserved in the geologic record.
Examples of Locations with Pillow Lava
Locations where pillow lava has been studied or is visible include:
– The mid-Atlantic Ridge, a mid-ocean ridge that runs down the center of the Atlantic Ocean.
– The Juan de Fuca Ridge off the northwest coast of North America.
– Iceland, where pillow lavas can be observed on the coast where the Mid-Atlantic Ridge rises above sea level.
– The Hawaiian Islands, especially where new lava flows from Kilauea or other active volcanoes enter the ocean.
The Difference Between Pillow Lava and Other Lava Types
Pillow lava is just one type of volcanic rock, and it is distinguished from others by its formation environment and texture.
Comparison with Aa and Pahoehoe Lava
Aa and pahoehoe are types of lava flows that occur on land, characterized by their surface texture and movement. Aa is rough and clinkery, while pahoehoe is smooth and ropy. By contrast, pillow lava has a much smoother, sometimes glassy exterior due to its rapid cooling in water, and it forms bulbous, interconnected lobes rather than extended flows.
Chemical Composition
The composition of pillow lavas is usually basaltic, meaning they are rich in iron and magnesium and relatively low in silica. This composition is common for lava that erupts at mid-ocean ridges and is characteristic of the oceanic crust.
Understanding Pillow Lava Through Modern Research and Monitoring
Advances in deep-sea exploration and monitoring technology, such as remotely operated vehicles (ROVs), have expanded our opportunities to observe pillow lavas as they form.
Modern Research Methods
Modern research methods include:
– Direct observation and sampling using ROVs.
– Seismic and sonar mapping to identify subsurface structures.
– Chemical analysis of rock samples to determine composition and temperature of formation.
– Laboratory simulations to replicate the process under controlled conditions.
Modern research continues to unravel the complexities of submarine volcanic activity and the role pillow lava plays in creating the crust that forms the ocean floor.
Finishing Thoughts
Pillow lava captures the imagination with its unique shapes and textures, providing a stark reminder of the powerful forces at work beneath the Earth’s oceans. As geologists and oceanographers continue to explore the undersea world, the study of pillow lavas remains a critical window into understanding our planet’s hidden processes and ancient history. Discovering and analyzing these strange, pillow-shaped rocks that lie on the ocean floor or within the layers of the Earth’s crust, not only satisfies human curiosity but also enhances our appreciation for the dynamic planet we inhabit.
