Volcanism
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Volcanism

World Organization of Volcano Observatories (WOVO)

The World Organization of Volcano Observatories was established as the result of a meeting of representatives from world-wide volcano observatories, held in Guadeloupe in 1981. WOVO became International Association of Volcanology and Chemistry of the Earth’s Interior Commission in the following year.

The principal aims of the World Organization of Volcano Observatories are:

1. To stimulate cooperation between scientists working in observatories and to create or improve ties between observatories and institutions directly involved in volcano monitoring.

2. To facilitate an exchange of views and experience in volcano monitoring by convening periodic meetings including field-based ones, by periodic newsletters, and by promoting a specific e-mail observatories network service.

3. To maintain an up-to-date inventory (Directory of Volcano Observatories) of networks and of instrumentation and manpower that could be made available to any of the member institutions if a situation arises that requires scientific support.

4. To supply technical support at observatories in developing countries and to create a WOVO fund to be used by these observatories (activities of WOVO generally speaking are focused on dangerous volcanoes in developing countries).

5. To organise an international task force and to promote funding from international organisations that could help defray travel and related expenses of scientific support teams.

Volcano Monitoring Techniques

Background:

Geologists have developed several methods to monitor changes in active volcanoes. These methods allow geologists to forecast and, in some cases, predict, the onset of an eruption. A forecast indicates that the volcano is „ready“ to erupt. A prediction states that a volcano will erupt within a specified number of hours or days (Wright and Pierson, 1992). Several methods developed by and currently used at the Hawaiian Volcano Observatory are introduced in the following paragraphs. The Teaching Suggestions provide additional description and activities.

How do Volcanologists predict volcanic eruptions?

The prediction of volcanic eruptions is difficult because, to be of practical use, they must be made before eruptions! Its a lot easier to see patterns in monitoring data after an eruption has occurred. But great progress has been made because of the lessons learned over many years at Kilauea volcano in Hawaii, and applied and modified at Mt. St. Helens before and during in eruption sequence in the 1980s.

Meaningful prediction requires careful monitoring of a volcano’s vital signs. Seismometers can be used to pinpoint earthquakes which track the rise of magma and its movement along fissures. Measurements of the tilt of the entire mountain provide additional information about the „breathing“ of the volcano as magma moves inside it. Instruments that sniff SO2, CO2 and other gases also can signal changes in the volcano. At some volcanoes the seismic information seems most reliable, at others the tilt tells the story. But the best predictions come from the combination of all of these methods into a volcano monitoring and prediction system.

You must remember that each volcano is unique. The pattern of events that signifies an eruption at one volcano may not occur before an eruption at a different volcano. And the same volcano may change its eruptive behavior at any time! The good news is that general trends in precursor behavior our being observed at a variety of volcanoes around the world so that volcanologists are getting better at predicting eruptions.

How does a thermocouple measure the temperature of lava without melting?

A thermocouple works on the principle that the electrical resistance at the point where two wires of different composition join, is very sensitive to the temperature. So…a thermocouple consists of two wires joined to an electrical source. Current passes through the wires and they only touch eachother out at the tip of the thermocouple probe. The temperature of that tip controls the resistance of the current passing through the place where they join, and this resistance can be measured and converted to temperature information. These little wires are usually sheathed in a ceramic insulation with an outer sheath of stainless steel. The melting points of stainless steel, ceramic, and the two wires are all higher than the temperature of lava, so none of them melt.

Lava

Background:

There are three types of lava and lava flows: pillow, pahoehoe, and aa. Pillow lavas are volumetrically the most abundant type because they are erupted at mid-ocean ridges and because they make up the submarine portion of seamounts and large intraplate volcanoes, like the Hawaii-Emperor seamount chain. Pahoehoe is the second most abundant type of lava flow.

Eruptions under water or ice produce pillow lava. James Moore of the U.S. Geological Survey made the first underwater observations of the formation of pillow lavas (Moore and others, 1973). Moore and his coworkers studied lava from the Mauna Ulu eruption They described pillow lavas as elongate, interconnected flow lobes that are elliptical or circular in cross-section (Moore, 1975). This photo shows pillow lava forming off the south coast of Kilauea volcano, Hawaii. Photograph by Gordon Tribble and courtesy of U.S. Geological Survey.

Lava flows near the coast tend to spread out laterally and enter the ocean
over a large front. Several lava tubes may be active across the flow front. Larger lava tubes feed down slope and maintain pressure in the growing lobes that extend into the water. Flow lobes develop most readily on steep slopes and result in stacks of pillow „tongues“ that parallel the offshore slope. This offshore stack of lava produces beds of rubble parallel to the offshore slope. Geologists call these steeply dipping beds foreset beds.

On November 8, 1992, lava entered the ocean just east of the archeological sites at Kamoamoa on the south flank of Kilauea volcano. By the end of the month, nearly all of Kamoamoa was buried under lava. By May 1993, a lava delta had extended the coastline about 1,600 feet (500 m) to the south. This aerial view is to the west. Photograph by Christina Heliker, U.S. Geological Survey, May 12, 1993.

The foreset beds are part of a lava delta that grows towards the ocean and provides a platform on which subaerial lavas can extend, thus adding new land to the island. However, some lobes are not continuous and break apart to form pillow sacks, thus adding rubble to the flank of the volcano. The active front of a lava delta is called a bench. Like the delta, the bench is built on rubble. However, the bench is relatively unstable and can collapse, falling into the ocean (Mattox, 1993).

A bench collapsed at the Lae Apuki entry in April 1993, removing a block 690 feet (210 m) long, 46 feet (14 m) wide, and 26 feet (8 m) thick from the front of the delta. A visitor, standing on the bench at the time of the collapse, disappeared into the ocean. This aerial view shows an active bench adding new land out from the old sea cliff (bottom of photo). Dark areas are black sand. Photograph by Christina Heliker, U.S. Geological Survey, August 25, 1994.

Pillow lavas are also found near the summit of Mauna Kea These pillow lavas were produced by a subglacial eruption that occurred 10,000 years ago. The pillow is about 3 feet (1 m) in diameter and has a glassy rim. Figure 21.11 from Porter, 1987.

Pillow lavas can also form when flows enter a river or lake. The pillows in the photo formed in the Wailuku River above Hilo, Hawaii about 3,500 years ago. The round cobbles were transported by the river. Photograph by Jack Lockwood, U.S. Geological Survey, June 14, 1982.

Pahoehoe lava is characterized by a smooth, billowy, or ropy surface. A ropy surface develops when a thin skin of cooler lava at the surface of the flow is pushed into folds by the faster moving, fluid lava just below the surface.

Pahoehoe flows can evolve into lava tubes. One way that tubes form is by the crusting over of channelized lava flows. As the crust on a flow becomes thicker, it insulates the lava in the interior of the flow. The lava drains down slope and feeds the advancing front or flows into the ocean. When the eruption stops or the vent is abandoned, the lava drains from the tube. Thurston lava tube is an excellent example of a lava tube. The rock surrounding a lava tube serves as a insulator to keep the lava hot and fluid. Because the lava remains hot, it can travel great distances from the vent. For example, tube-fed pahoehoe lava traveled 7.3 miles (11.7 km) from the Kupaianaha vent to the village of Kalapana (Mattox and others, 1993). Photo of volcanologist looking through a skylight to see inside of a lava tube. Photograph by J.D. Griggs, U.S. Geological Survey, February 2, 1989.

Pahoehoe flows tend to be relatively thin, from a few inches to a few feet thick. Road cuts and craters expose stacks of lava flows that make the volcano.

Aa is characterized by a rough, jagged, spinose, and generally clinkery surface. Aa flows advance much like the tread of a bulldozer. This photo is looking across an aa channel. Note the character of the aa that makes the wall of the channel. Photo by Steve Mattox, October 12, 1990.

The interior of the flow is molten and several feet thick. The molten core grades upwards and downwards into rough clinkers. As the flow advances, clinker on the surface is carried forward relative to the molten interior. The clinkers continue to move forward until they roll down the steep front. The clinkers are then overridden by the molten core. Aa lava flows tend to be relatively thick compared to pahoehoe flows. Aa flows from the 1984 Mauna Loa eruption ranged from 6 to 23 feet (2-7 m) in thickness.

During the early episodes of the current eruption, aa flows up to 36 feet (11 m) thick surged through the Royal Gardens subdivision at rates as great as 108 ft/min (33 m/min)(Neal and Decker, 1983). The molten core of the flow is exposed. Note vehicles for scale. Photograph by R.W. Decker, U.S. Geological Survey, July 2, 1983.

Since the mid-1800s, geologists have tried to explain the causes of pahoehoe and aa lava. Several factors were offered to explain the transition: impediment of flow by obstacles, flowage during cooling, quantity of lava, conditions under the flow, and deep cooling. In the last few decades, with careful observations of numerous lava flows, geologists have reached a better understanding of the transition of pahoehoe to aa. One important influence is the viscosity of the lava. Viscosity is the resistance of a fluid to flow. For example, molasses has a higher viscosity that water. The following paragraphs outline some of the more important observations on the transition of pahoehoe to aa.

How is lava formed?

First, there is a definition we need to make. Just to
things straight, geologists use the word „magma“ for molten rock that is still underground, and the word „lava“ when it has reached the surface.

Rocks in the mantle and the core are still hot from the formation of the Earth about 4.6 billion years ago. When the Earth formed, material collided at high speeds. These collisions generated heat (try clapping your hands together – they get hot) that heat became trapped in the Earth. There is also heat within the earth produced by radioactive decay of naturally-occurring radioactive elements. It is the same process that allows a nuclear reactor to generate heat, but in the earth, the radioactive material is much less concentrated. However, because the earth is so much bigger than a nuclear power plant it can produce a lot of heat. Rocks are good insulators so the heat has been slow to dissipate.

This heat is enough to partially melt some rocks in the upper mantle, about 50-100 km below the surface. We say partially melt because the rocks don’t completely melt. Most rocks are made up of more than one mineral, and these different minerals have different melting temperatures. This means that when the rock starts to melt, some of the minerals get melted to a much greater degree than others. The main reason this is important is that the liquid (magma) that is generated is not just the molten equivalent of the starting rock, but something different.

You could think of making a „rock“ out of sugar, butter, and shaved ice. Pretend that they are mixed equally so that your rock is 1/3 sugar, 1/3 butter, and 1/3 shave ice. If you start melting this „rock“, however, the „magma“ that is generated will be highly concentrated in the things that melt more easily, namely the ice (now water) and butter. There will be a little bit of molten sugar in your magma, but not much, most of it will still be crystalline.

The most common type of magma produced is basalt (the stuff that is erupted at mid-ocean ridges to make up the ocean floors, as well as the stuff that is erupted in Hawai’i). Soon after they’re formed, little drops of basaltic magma start to work their way upward (their density is slightly less than that of the solid rock), and pretty soon they join with other drops and eventually there is a good flow of basaltic magma towards the surface. If it makes it to the surface it will erupt as basaltic lava.

What is lava made of?

Lava is made up of crystals, volcanic glass, and bubbles(volcanic gases). As magma gets closer to the surface and cools, it begins to crystallize minerals like olivine and form bubbles of volcanic gases. When lava erupts it is made up of a slush of crystals, liquid, and bubbles. The liquid „freezes“ to form volcanic glass.

Chemically lava is made of the elements silicon, oxygen, aluminum, iron, magnesium, calcium, sodium, potassium, phosphorus, and titanium (plus other elements in very small concentrations. Have a look at the background information in Minerals, Magma, and Volcanic Rocks.

Chemistry:

Most rocks are made of the following elements:

Element (Symbol)

Weight percent

Oxygen (O) 46.6

Silicon (Si) 27.7

Aluminum (Al) 8.1

Iron (Fe) 5.0

Calcium (Ca) 3.6

Sodium (Na) 2.8

Potassium (K) 2.6

Magnesium (Mg) 2.1

Total: 98.5

The amount of these different elements in a rock can be determined. Geologists report the values as oxides (the element combined with oxygen). For example, a rock might have 6 weight percent FeO (iron oxide).

Different types of lava have different chemical compositions.

How does lava change its composition?

Geochemists use several elements to track the history of a batch of magma. For our example we’ll start with magnesium (and think of it as magnesium oxide, MgO, like the geochemists do). Beneath Hawaii, when the mantle melts it produces a magma with about 17 weight percent MgO. Volcanologists call magma with this composition a picrite. As the magma rises crystals begin to form. The first crystal to form is olivine, which contains the elements magnesium, silicon, and oxygen in the proportions 2 to 1 to 4. The crystal is more dense than the surrounding magma and it begins to settle. It is estimated that an than the surrounding magma and it begins to settle. It is estimated that an olivine crystal 1 mm in diameter falls through the magma at a rate of 20 meters per hour. By settling the crystals are being removed from the magma, causing the chemical composition of system to change. As more and more olivine crystals settle, the magma has less and less magnesium oxide and more and more silica. For most volcanoes, by the time the original magma from the mantle is erupted its composition has changed from a picrite to a basalt.

If the magma is not erupted, the same process continues but more and different minerals become involved. In general, the removal of these crystals drives the composition away from that of a basalt and towards that of a rhyolite. The amount of magnesium oxide and iron oxide continues to decrease and the amount of silica, sodium oxide, and potassium oxide increases.

Other processes can become involved. The magma may melt and incorporate crustal rocks that tend to contain more silica. This drives the composition towards rhyolite. The rising magma may also intersect and mix with a magma that has evolved differently. This will also change its composition.

These processes (crystal settling, assimilation, and magma mixing) influence the composition of the magma. Geochemists
study the minerals and the chemistry of the lava to determine which processes were involved and how big of a role each one played.

How hot is lava?

The temperatures of lavas vary depending on their chemical composition. Hawaiian lava (basalt) is usually around 1100 C. Volcanoes such as Mt. St. Helens erupt lava that are around 800 C.

Here is a list of temperatures for the common types of lava:

Rock type

Temperature (C) Temperature (F)

Rhyolite 700-900 1292-1652

Dacite 800-1100 1472-2012

Andesite 950-1200 1742-2192

Basalt 1000-1250 1832-2282

How long does it take lava to cool?

Lava cools very quickly at first and forms a thin crust that insulates the interior of the lava flow. As a result, basaltic lava flows can form crusts that are thick enough to walk on in 10-15 minutes but the flow itself can take several months to cool! Because of the insulating properties of lava, it cools slower and slower over time. Thick stacks of lava flows (30 m or 100 ft thick) can take years to cool completely. An extreme example is a lava flow that was erupted in 1959 and partly filled a pit crater (Kilauea Iki). The „ponded“ flow was about 85 meters thick (about 280 ft thick). It was drilled in 1988, and there was still some mushy, not-quite-solid stuff down near the bottom, 29 years after it erupted!

How far can lava flow?

The longest recent flow in Hawai’i was erupted from Mauna Loa in 1859. It is about 51 kilometers long from the vent to the ocean (we don’t know how much longer it went out under water, but probably not too much farther). There is a lava flow at Undara in Queensland, Australia is 100 miles (160 km) long.

How fast does lava flow?

In Hawaii the fastest flows we’ve recorded were those of the 1950 Mauna Loa eruption. These were going about 6 miles (10 kilometers) per hour through thick forest. That was the velocity of the flow front. Once the lava flows became established and good channels developed, the lava in the channels was going at more like 60 km/hour!

On January 10,1977, a lava lake at Nyiragongo drained in less than one hour. The lava erupted from fissures on the flank of the volcano and moved at speeds up to 40 miles per hour (60 km/hr). About 70 people were killed.

How close can I get to lava and will it hurt or kill me?

How close you can get depends on what kind of lava flow it is, and whether you are upwind or downwind. For example, the most approachable lava is pahoehoe. This is because each toe forms an insulating skin seconds after emerging on the surface. This skin is at first flexible and then hardens, but even when flexible it is a good insulator. This serves to keep the interior of an active pahoehoe toe hot and fluid but also prevents you from getting burned by the radiant heat. If the wind is at your back, you can easily approach long enough and close enough to get a sample with a hammer. It is still hot, and unless yo! are well-protected you can only be that close for a minute or so. You also notice that as soon as you peel the skin off to get at the molten interior, th! heat goes way up. This is heat that you can’t stand, you have to get back otherwise blisters start to form. It is hot enough that you can’t accidentally step on active lava.

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