Volcanic Ash : Rabaul Caldera, Papua New Guinea (Lauer, 1995)

Volcanic Ash : Rabaul Caldera, Papua New Guinea (Lauer, 1995)

Aerial view of Rabaul Town covered in volcanic ash, Papua New GuineaFollowing a 27-hour period of intense earthquake activity, Tavurvur and Vulcan volcanoes on opposite sides of the Rabaul caldera erupted on September 19, 1994, early in the morning. Nearby Rabaul Town (right, click for large-sized image) was covered with volcanic ash as thick as 1.5 m, and an estimated 90,000 people were displaced from the area.

"The volcanic ash was mushrooming out in thick clouds-but there was no noise. The earth had stopped moving. It was 6.15 am. We watched in awe. The clouds began to drift towards us... What a tremendous experience! But now the sky was darkening and black specks of ash were falling on us like light rain. There was also an overpowering small of sulphur."

7.30 am, after driving to a new location, about 8 km (5 mi) from Rabaul town. "Soon the clouds would reach Kulau too. Suddenly there were fears of being overcome by poisonous gas. The smell of sulphur was sickening and the air was a strange, yellowish colour. The the power went off. In a moment of panic, people, including our party which had now increased to eleven, decided to head for the safety of Kerevat, using the North Coast Road. Progress was extremely slow as the road was choked with half the population of Rabaul, all with the same idea. Eventually the vehicle traffic halted altogether. Due to unusual thermal patterns Kerevat was deluged by mud rain and the road quickly became impassable." The party returned to Kulua.

"The next day brought much of the same-but it seemed to drag on and on. The atmosphere was very heavy. There was no power. Every time we left the house we collected volcanic ash and pumice on our skin and in our hair. And the noise-the thunder and lightning was constant, with some almighty cracks. It was obvious that objects were being struck."

Five days later, describing a visit home to retrieve belongings: "There were parts of trees all over the road, flattened vegetation everywhere and everything covered in ash and mud. Our houseyard looked like a moonscape—house, water tanks, plants—all a drab grey. The trees along the bank had snapped and lost most of their foliage... inside the house was a depressing mess. The floors were covered in volcanic ash. There was even ash on the ceiling above the louvres and caked along the top of the curtains."

Nine days after the eruption: "The volcanic ash was dreadful all day yesterday. It was clearly visible in the air and I could feel and see it on my skin every time I stepped outside. I can't get used to wearing the mask and goggles. I found the smell of the masks nauseating so I've taken to wearing a folded handkerchief over my nose and mouth like a "baddie" in a Western movie."

AVolcanic Ash : Mount St. Helens, Washington

AVolcanic Ash : Mount St. Helens, Washington

"By noon, the City was engulfed in darkness by volcanic ash and communications by home telephone were impossible. It was like an eclipse of the sun that lingered, a blinding blizzard and an electrical storm all in one. Light-sensitive street lights came on automatically, traffic stopped, and a strange quiet fell on our community; and everywhere a talcum-like sandy gray powder kept accumulating. Cars, trucks, buses, and trains, all stopped, and planes were re-routed away from the ash cloud."

"From noon until 6:00 a.m. the following morning, the City was in total darkness. Three types of ash fell alternatively on the City: dark gray sand, medium gray sand, and a light gray cement-like dust. All three grades were gritty and light, difficult to sweep or shovel, especially when dry. To make matters worse, shifting winds blew the ash everywhere, severely impairing visibility and driving in our area. It was exceedingly harmful and abrasive to mechanical and electrical equipment, especially motors of vehicles, aircraft and electronic systems. Unlike snow, however, this "precipitation" was not going to melt!"

"The volcanic ash fall was especially crippling—Yakima received 5-8 cm (2-3 in) of this material in the first 24 hours following the explosion. We estimated that several million tons of volcanic ash was deposited on the entire region."

What's it like during an ash fall?

What's it like during an ash fall?

When ash begins to fall during daylight hours, the sky will turn increasingly hazy and "dusty" and sometimes a pale yellow color. The falling volcanic ash may become so dense that daylight turns to murky gray or even an "intense blackness" such that "it is impossible to see your hand when held up close to the eye." Loud thunder and lightning and the strong smell of sulfur often occurs during an ash fall. Furthermore, rain may accompany the volcanic ash and turn the tiny particles into a slurry of slippery mud. Most people also describe an intense quietness, except for thunder that may accompany the ash fall, giving a "deadness" to the normal sounds of life.

Volcanic Ash falls vary widely in intensity, size of the ash particles, and the degree to which light from the sun is obscured or blocked completely. Because of the unexpected darkness during daylight hours, loud thunder and lightning, and the sometimes strong smell of sulfur during a volcanic ash fall, many people describe the experience as eerie and frightening, disorienting and confusing, or dreadful. In extreme ash fall, for example when ash thickness is more than 5-10 cm (2-4 in), people may feel stunned and fearful of the conditions, have a difficult time breathing if a well-sealed shelter is not available. If caught outside during low visibility, people may become lost or extremely disoriented.

If heavy volcanic ash fall continues for 12-60 hours or more, roofs may collapse under the weight of the ash, resulting in more confusion, injuries, and even death.

Knowing what to expect during and after an ash fall can help people (1) reduce their anxiety and uncertainty when ash is falling to the ground; and (2) prepare their families and communities to deal with the ash effectively.

VOLCANIC ASH 1

Volcanic Ash 1

Volcanic ash is a volcanic rock which is exploded from a vent in fragments less than 2mm in size. Volcanic ash-particles are like small sharp glass-particles that damage anything they come across. Because volcanic ash can fall on many things it's very harmful to the environment around the volcano. During heavy ash-rains houses and buildings may collapse, people and animals may die by lack of oxygen.

Ash clouds may provide big problems for aviation. When airplanes fly through an eruption cloud a range of damage may occur depending on the concentration of volcanic ash, gas aerosols in the cloud and the actions taken by the pilot to exit the eruption cloud.
volcanic-ash.

Volcanic Ash

Volcanic Ash

Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than 2 millimetres (0.1 in) in diameter.

There are 3 mechanisms of volcanic ash formation:

• gas release under decompression causing magmatic eruptions;
• thermal contraction from chilling on contact with water causing phreatomagmatic eruptions,
• ejection of entrained particles during steam eruptions causing phreatic eruptions.

The violent nature of volcanic eruptions involving steam results in the magma and solid rock surrounding the vent being torn into particles of clay to sand size. Volcanic ash can lead to breathing problems and malfunctions in machinery, and clouds of it can threaten aircraft and alter weather patterns.

Ash deposited on the ground after an eruption is known as ashfall deposit. Significant accumulations of ashfall can lead to the immediate destruction of most of the local ecosystem, as well the collapse of roofs on man-made structures. Over time, ashfall can lead to the creation of fertile soils. Ashfall can also become cemented together to form a solid rock called tuff. Over geologic time, the ejection of large quantities of ash can produce an ash cone.