# Volcanoes/Volcanic activity

Volcanic activity may be activity from or by a volcano or activity from the sources of volcanoes.
On Iceland this year there is an increase in volcanic activity as shown in the photo on the right.
"Our research makes the connection between recent accelerated uplift and the accelerated melting of the Icelandic ice caps."
"There is actually geological evidence that during the past deglaciation about 12,000 years ago, volcanic activity in some regions of Iceland increased thirtyfold. In fact, some estimate that this uplift could increase the frequency of volcanic eruptions such as the 2010 eruption of Eyjafjallajokull, which had negative consequences worldwide."

## Activity

Def. "the quality or state of [...] causing change" is called activity.
"The lava [from the Villarrica volcano on the right] traveled down the slopes of the 9,380-foot high volcano, melting snow along the way and creating mudflows."

## Volcanic

Def.
* of "or pertaining to a volcano or volcanoes",
* produced "by a volcano, or, more generally, by igneous agencies", or
* changed "or affected by the heat of a volcano"
is called volcanic.
"This is one of the more spectacular volcanic eruptions the world has seen lately [imaged on the right]. Early in the morning on March 3, Villarrica in Chile erupted, sending ash and lava flying some 3,300 feet up into the atmosphere."
"The eruption caused nearly 4,000 people to flee the surrounding areas, including from the nearby tourist town of Pucón, though the BBC reports that residents mostly left "calmly." After about 20 minutes, the volcano piped back down, and the nearby towns seemed okay."
"Villarica is one of Chile's most active volcanoes and, according to the Smithsonian's Global Volcanic Program, is one of three tall stratovolcanoes in a chain that runs perpendicular to the Andes mountain range, believed to be caused by a fracture in the Earth's crust."

## Gases and ash columns

"During a visit to the Colca Valley, the Minister of Defense of Peru was able to observe, in a flyby, the columns of gases and ash that rise from the crater of the Sabancaya, which according to the Geophysical Institute of Peru (IGP) have a height of approximately 3,200 meters."
"In addition, according to the reports of this scientific entity, the volcano currently has an explosive activity of moderate levels, with an average of 44 explosions per day in the last week. The dispersion of gases and ash reaches a radius greater than 40 kilometers."

## Eruption clouds

In the photo on the right, Villarrica volcano can be seen erupting clouds on March 3, 2015, especially exhibiting fiery hot ejecta composing the base and lower portion.
Def. "a column of ash emitted during a volcanic eruption" is called an eruption column.
The solid and/or liquid materials in an eruption column are lifted by processes which vary as the material ascends:
* At the base of the column, material is violently forced upwards out of the crater by the pressure of rapidly expanding gases, mainly steam. The gases expand because the pressure of rock above it rapidly reduces as it approaches the surface. This region is called the gas thrust region and typically reaches to only one or two kilometers above the vent.
* The convective thrust region covers most of the height of the column. The gas thrust region is very turbulent and surrounding air becomes mixed into it and heated. The air expands, reducing its density and rising. The rising air carries all the solid and liquid material from the eruption entrained in it upwards.
* As the column rises into less dense surrounding air, it will eventually reach an altitude where the hot, rising air is of the same density as the surrounding cold air. In this neutral buoyancy region, the erupted material will then no longer rise through convection, but solely through any upward momentum which it has. This is called the umbrella region, and is usually marked by the column spreading out sideways. The eruptive material and the surrounding cold air has the same density at the base of the umbrella region, and the top is marked by the maximum height which momentum carries the material upward. Because the speeds are very low or negligible in this region it is often distorted by stratospheric winds.

## Lava fountains

On the right is "a close-up of the lava fountains" from the March 3, 2015, eruption of Villarrica volcano in Chile.
"Villarica is one of Chile's most active volcanoes and, according to the Smithsonian's Global Volcanic Program, is one of three tall stratovolcanoes in a chain that runs perpendicular to the Andes mountain range, believed to be caused by a fracture in the Earth's crust."
On the left: "A jet of lava sprayed into the air by the rapid formation and expansion of gas bubbles in the molten rock is called a lava fountain. Lava fountains typically range from about 10 to 100 m in height, but occasionally reach more than 500 m. Lava fountains erupt from isolated vents, along fissures, within active lava lakes, and from a lava tube when water gains access to the tube in a confined space [...]."
"Kīlauea's current eruption is a natural laboratory for volcanologists Tephra falling from a lava fountain on September 6, 1983, helped build the Pu‘u ‘Ō‘ō cone, which eventually reached a maximum height of 255 m (835 ft) in 1986."

## Lava lakes

"Most of the time, though, the volcano is a popular destination for hikers, who climb the 9,380-foot high mountain during the summer months to peer at the lava lake in its crater."
Def. a "reservoir of molten lava contained in a volcanic vent, crater, or broad depression" is called a lava lake.
The image on the right shows a lava lake occurring in the caldera of the Villarrica volcano in Pucon, Chile, that is raging during the volcano's eruption.
On the left is the relatively quiescent lava lake of the Nyiragongo Volcano.

## Lahars

"Because the volcano itself is covered by 15 square miles of glaciers, the lava that flows down the side and mixes with ice and snow to form lahars — a mudflow slurry that can move extremely quickly and destroy towns in their path. According to the Smithsonian, "lahars have damaged towns on Villarica's flanks." The BBC reports that more than 100 people are believed to have been killed by the volcano's mudflows in the past century."
Def. a "volcanic mudflow" is called a lahar.
Part of the Mount St. Helens lahar entered Spirit Lake (lower left corner of the image on the right) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 50 miles (80 kilometers) downstream.

## Lightning

On the right is an image of the Villarrica volcano erupting near Pucon, Chile, March 3, 2015, with lightning striking apparently the lower back of the eruption cloud with few leaders.
Many volcanic eruptions put on impressive lightning displays such as during the 1995 eruption of Mount Rinjani in Indonesia shown in the image on the right which exhibits many leaders.
The image on the left shows spectacular lightning strikes around Galunggung, including multiple leaders apparently involved in cloud to cloud lightning.
"This stratovolcano with a lava dome is located in western Java. Its first eruption in 1822 produced a 22-km-long mudflow that killed 4,000 people. The second eruption in 1894 caused extensive property loss. The photo depicts a spectacular view of lightning strikes during a third eruption on December 3, 1982, which resulted in 68 deaths. A fourth eruption occurred in 1984."
Volcanic lightning arises from colliding, fragmenting particles of volcanic ash (and sometimes ice), which generate static electricity within the volcanic plume. Volcanic eruptions have been referred to as dirty thunderstorms due to moist convection and ice formation that drive the eruption plume dynamics and can trigger volcanic lightning. But unlike ordinary thunderstorms, volcanic lightning can also occur before any ice crystals have formed in the ash cloud.
The earliest recorded observations of volcanic lightning are from Pliny the Younger, describing the eruption of Mount Vesuvius in 79 AD, “There was a most intense darkness rendered more appalling by the fitful gleam of torches at intervals obscured by the transient blaze of lightning.” The first studies of volcanic lightning were also conducted at Mount Vesuvius by Professor Palmieri who observed the eruptions of 1858, 1861, 1868, and 1872 from the Vesuvius Observatory. These eruptions often included lightning activity.
A famous image of the phenomenon was photographed by Carlos Gutierrez and occurred in Chile above the Chaiten Volcano. It circulated widely on the internet. Another notable image of this phenomenon is "The Power of Nature", taken by Mexican photographer Sergio Tapiro in Colima, Mexico, which won third place (Nature category) in the 2016 World Press Photo Contest. Other instances have been reported above Alaska's Mount Augustine volcano, Iceland's 2010 eruptions of Eyjafjallajökull volcano and Mount Etna in Sicily, Italy.

## Tufa

Def. "the calcareous deposit of lime found near hot springs" is called tufa.
The image on the right shows Mono Lake's "South Tufa".
"Tufa towers in Mono Lake are calcium carbonate spires and knobs formed by interaction of freshwater springs and alkaline lake water. Tufa can reach heights of 30 ft. (9.1m). Mono Lake is located is Eastern Sierra Nevada and covers about 65 square miles. Throughout the lake's existence of over 1 million years, the steady evaporation of freshwater originally coming from Eastern Sierra streams has left the salts and minerals behind so that the lake is now about 2 1/2 times as salty and 80 times as alkaline as the ocean."

## Tuff

Def. a "light porous rock, now especially a rock composed of compacted volcanic ash varying in size from fine sand to coarse gravel" is called tuff.

## Hypotheses

* Every 10° of longitude has at least one form of volcanic activity.