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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.