Bring a flashlight and water and don’t take any of the lava rock. Those were the guidelines my husband and I were given in 2002 prior to walking on the Kilauea volcano. It was active then, but nothing like it is today. However, the volcano captivated me and left a memorable impression.

At the time, I didn’t know there were different types of volcanoes. I expected a tall cone to spew lava like my fifth-grade science fair project. Instead, the volcano was relatively flat with multiple cracks and tunnels that flowed into the ocean.

As we walked out in the black of night, we crossed fissures that glowed bright, red with lava deep beneath. It was intensely hot. The experience was both exhilarating and terrifying at the same time.

Many Hawaiians believe the fire goddess, Pele, created the Hawaiian Islands and governs the Kilauea volcano, controlling the lava flow. Legend warns visitors who remove volcanic rock will suffer her wrath. Countless visitors testify to experiencing bad fortune after doing so and eagerly return Pele’s precious volcanic material.

There are about 1500 active volcanoes worldwide in addition to those under the ocean. Approximately one third of these have erupted in the past 100 years. Scientists have identified 169 volcanoes in the United States that are expected to erupt at some time. Most are in Alaska where eruptions occur nearly every year. The remainder are in the West and Hawaii.

The Kilauea volcano in Hawaii is one of the most active on Earth. It has been erupting since 1983. The eruption of Katmai Volcano in Alaska in 1912 is said to have been the most violent eruption to occur within the United States.

Volcanoes are openings or vents where lava (molten rock after it erupts above the Earth), tephra (small lava rock), and steam erupt on the Earth’s surface. Volcanic terrain is built by the slow accumulation of lava. The vent may be visible as a depression at the top.

Through a series of cracks within and beneath the volcano, the vent connects to one or more linked storage areas of molten rock made of oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese. This connection to fresh magma (molten rock, crystals, and dissolved gas below the surface of Earth) allows the volcano to repeatedly erupt in the same location increasing its size until it is no longer stable.

Magma originates tens of miles beneath the ground. It is driven upwards by buoyancy because it is lighter than the surrounding rock. Magma may erupt by pouring from vents as fluid lava flows or shoot violently into the air as dense clouds of rock shards and gas. Ash (shards of tephra) then may be carried in the wind around the world.

Volcanoes are categorized by their shape and size. Cinder Cone volcanoes are the smallest and are made of small pieces of solid lava.

Composite Volcanos, also called Stratovolcanos, form the largest mountains. These volcanoes have steep, even sides made from repeating layers of lava flows, volcanic ash, cinders, blocks, and volcanic bombs. The tallest composite volcano on Earth is the Ojos del Salado in Chile with a summit elevation of 22,615. The tallest in the United States is Mount Rainier in Washington State with a summit elevation of 14,410.

Shield Volcanoes are built almost entirely of fluid lava flows. They have a sloping dome shape similar to a warrior’s shield. They were built slowly by the growth of thousands of lava flows over great distances and cooling in thin sheets. The Hawaiian Islands are made of a chain of shield volcanoes which include Kilauea and Mauna Loa.

Lava Domes are technically lava flows but contain lava that is too thick to flow away from the vent and therefore squeeze out and accumulate as a giant pile over and around the vent. Lava domes may look like pointy spines, a giant muffin, flower petals opening, or as tongues.

Modern science provides warnings in advance of eruptions to assist in the preservation of human life but can do little to protect homes, farms, and businesses in the event of eruption. Magma contains dissolved gases which provide the driving force of most volcanic eruptions. Even if magma never reaches the surface, gases can continuously escape into the atmosphere from the soil and vents.

The most abundant volcanic gas is water vapor, which of course, is harmless. But significant amounts of carbon dioxide, hydrogen sulfide, and hydrogen halides also are emitted, all of which are potentially hazardous to plant, animals, property, and people. Also, in ash producing eruptions, ash is often coated with hydrogen halides. This can poison drinking water supplies, agricultural crops, and grazing land.

For more information, check USGS, Volcano Discovery, and USGS volcanic videos .

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