What are Some Types of Lava Formations?

When volcanoes explode, various interesting lava formations and features are often created. The most simple is new land -- created when volcanoes dump magma into the sea and it cools, forming rock. This process is ongoing in the Hawaiian Islands, where new land is created every year. Entire island chains, such as the Hawaiian Islands and much of Indonesia, are huge lava formations created tens of millions of years ago.

Another type of lava formation are lava tubes, which are formed when lava flows over the ground and the top of the flow hardens, sealing in super-hot lava which flows quickly through the tube. Lava tubes can either be active, as some are on the island of Hawaii, or dormant, as most around the world. These tubes are unique cave-like channels that can be explored by the adventurous. Their ceilings occasionally have lavacicles, lava formations created when hot lava splashes against the ceiling and drips down into a stalactite shape as it cools.

There are many unique rocks that are lava formations. These include Pele's hair, a thread-like golden rock created when wind blows airborne magma, lengthening it into fibers that look like strands of hair; Pele's tears, teardrop-shaped smooth rocks also created when airborne magma cools; obsidian, a glass-like black stone formed from cooling lava that has historically been used for axes and arrowheads; rhyolite, a light-gray mineral that forms from highly polymerized and viscous lavas; and pumice, a lightweight stone formed from frothy lavas that has such low density that it can often float on water.

Some of the largest surface objects in the world are lava formations, including the entire island of Hawaii, which, when measured from the sea floor, can be considered the tallest mountain in the world, even taller than Mt. Everest. Other lava formations, called traps or large igneous provinces, may be over a mile thick and cover hundreds of thousands of square miles. These distinct rocks form during catastrophic volcanic events that expel over a million cubic miles of magma onto the Earth over a period of as long as a million years. These events have been historically associated with mass extinctions, including the most severe mass extinction in the history of the planet, which wiped out about 95% of all living species.

Lava flows can be broadly categorized into two types: pahoehoe and a'a. Pahoehoe flows are characterized by a smooth, billowy, or ropy surface and are typically less viscous, allowing them to flow more easily. In contrast, a'a flows are much thicker and cooler, with a rough, jagged surface composed of broken lava blocks called clinkers.

Lava tubes are natural conduits formed by flowing lava which moves beneath the hardened surface of a lava flow. They form when the outer edges of a lava flow cool and solidify, while the molten lava beneath continues to flow. When the lava flow stops, it leaves behind an empty tunnel, which is the lava tube.

A lava tree is a unique geological formation that occurs when lava engulfs a tree. The moisture in the tree cools the lava rapidly, creating a mold around the tree. As the tree burns away or decomposes, it leaves behind a hollow, vertical lava cast, which resembles the original shape of the tree.

A lava dome is a mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Lava domes grow by the expansion from within, and their growth can be accompanied by explosive activity. They are often composed of rhyolite or dacite, which are more silica-rich than basaltic lavas.

Pillow lavas are typically found underwater and are formed when lava erupts on the ocean floor. As the hot lava makes contact with the cold water, it cools rapidly, creating a distinctive pillow-shaped structure. These formations are important as they indicate past underwater volcanic activity and can influence ocean topography.

Volcanic bombs are large blobs of molten rock that are ejected during an explosive volcanic eruption. They differ from other lava formations as they are airborne fragments, not ground flows. As they travel through the air, they cool and solidify, landing in a variety of shapes, some streamlined in form due to their flight.