Pillow lava is a unique type of lava formation typically found underwater, particularly along mid-ocean ridges, subduction zones, and seamounts. It is characterized by a series of interconnected, rounded blobs, or “pillows,” which form as the molten rock emerges from the Earth’s crust into the cold ocean water and quickly solidifies. The rapid cooling causes the outer layer of lava to become a glassy crust, encapsulating the still-flowing hot lava within. Pillow lavas are an important feature in understanding the geologic activity of underwater environments and are indicative of submarine volcanic activity.
Understanding Pillow Lava Formation
When lava with low to intermediate viscosity, usually basaltic in composition, erupts under water, it behaves differently than lava that erupts onto land. The abrupt temperature difference between the hot lava and the cold sea water creates a distinctive solid crust almost immediately around the lava flow. As more lava pushes through the crust, it inflates and stretches the solid shell, sometimes causing it to crack and form another pillow, thus the lava grows in a stack or chain-like formation, one pillow at a time, giving it a remarkable and identifying appearance.
Stages of Pillow Lava Development
The formation of pillow lava can be described in several stages:
1. Extrusion Stage: Lava is extruded into the cold water, creating an initial crust around the flow due to the rapid cooling.
2. Inflation Stage: Additional lava flows into the newly formed crust, inflating it until it resembles a pillow shape.
3. Budding Stage: The pressure builds until the crust cracks, and lava squeezes out, starting the formation of a new pillow next to or on top of the previous one.
4. Solidification Stage: The lava flow eventually stops, and the newly formed pillows cool and solidify completely.
The physical characteristics of pillow lavas also depend on the depth at which they are formed. At greater depths, increased water pressure can lead to smaller, more closely packed pillows, while in shallower waters, pillows may be larger and more spread out.
The Composition and Structure of Pillow Lavas
The classic composition of pillow lavas is basaltic, which is a fine-grained igneous rock rich in iron and magnesium. This type of lava is fluid at high temperatures, allowing it to spread out and form pillows. Upon cooling, pillow lavas often exhibit a radial jointing pattern where cracks radiate outward from the center of the pillow formation. The interiors of pillows can be vesicular, containing gas bubbles that were trapped as the lava solidified.
Surface Features and Glassy Outer Layer
The surface of pillow lavas is unique in its texture, due to the glassy rind that results from the quenching effect of water. This outer layer can be smooth, fractured, or ornamented with striations and grooves that reflect the flow directions just before solidification. Below the glassy surface, the rock may be more coarse and crystalline.
Environmental Significance of Pillow Lavas
Pillow lavas play an important role in shaping the oceanic topography. They contribute to the construction of the oceanic crust and are often associated with geological hotspots, which are areas where plumes of hot mantle material rise towards the Earth’s surface. These hotspots can result in high levels of volcanic activity that produce extensive pillow lava formations.
Habitat Creation
Pillow lavas can also form unique habitats for marine life. The nooks and crannies between pillows offer shelters for a variety of marine organisms, creating ecological niches and contributing to the biodiversity of the ocean floor.
Studying Pillow Lavas
Scientific study of pillow lavas has provided insightful information on the dynamics of Earth’s geology. The study often involves direct observation, using remotely operated vehicles (ROVs) or manned submersibles to explore and visually document the ocean floor. Samples of pillow lavas are also collected for laboratory analysis, which can tell us about their chemical composition, the conditions under which they formed, and the age of the geological structures they comprise.
Invaluable to Plate Tectonics Theory
Pillow lava formations are critical to understanding the process of seafloor spreading and the theory of plate tectonics. By analyzing the orientation and distribution of pillow lavas, scientists can infer past movements of tectonic plates and the formation of various features such as mid-ocean ridges and island arcs.
Indicators of Underwater Volcanism
Pillow lavas are one of the most apparent indicators of underwater volcanism. While still primarily studied in ocean settings, pillow lavas can also be found in ancient terrains where prehistoric oceans once existed. As these oceans receded or as tectonic plates shifted, areas of pillow lavas emerged above sea level, preserved in the geological record.
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On land, pillow lavas present compelling evidence of past geological processes and environments that can be millions or even billions of years old. By dating these formations, geologists can piece together the history of the Earth’s surface and the movements of its tectonic plates over time.
Impact on Human Activity
While not directly affecting daily human activities, the presence of pillow lavas can have significant impacts on projects such as the laying of submarine cables or the construction of off-shore drilling platforms. The rough and uneven terrain created by pillow lava formations can pose challenges that require careful planning and engineering solutions.
Potential for Hydrothermal Systems
Pillow lavas can also be associated with hydrothermal systems, where seawater circulates through hot volcanic rocks and emerges as heated, mineral-rich vents. These systems are of interest for mining operations due to the concentrations of valuable minerals such as copper, gold, and zinc that can accumulate in these areas.
Finishing Thoughts
Pillow lavas represent a fascinating intersection of geology, oceanography, and biology. Their distinctive appearance, coupled with the role they play in the dynamics of the Earth’s crust, make them a subject of ongoing study and interest. By examining pillow lavas, scientists not only glean valuable information about past and present geological processes but also about the potential resources and hazards beneath the ocean’s surface. As we continue to explore the hidden realms of our planet, these intriguing formations will undoubtedly provide further insights into the pristine environment of the deep sea and the perpetual evolution of our planet’s geology.
