- In a volcanic eruption, gases try to escape, which forces rock to crack and break. These cracked rock fragments heat up and are forced into the air and recede again in the form of ash. This heavy material can compact like snow fall and can cause much damage because of its weight.
Tephra Block From Mt St Helens. This rock was lava, before it was thrown into the air and cooled on its way back down to the earth.
Tephra are fragments of volcanic rock that are forced into the air by massive explosions from fishers. Tephra ranges in size from 2mm –
1m in diameter. Wind can carry tephra to surrounding areas of the volcano.
------------The ash fallout of the Mt. St. Helens eruption.
A pyroclastic flow is a large cloud of steaming rock fragments that are forced into the air because of the initial volcanic explosion. The fiery hot material rushes back down the side of the volcano like an avalanche. With great force and speeds of up too 100km/hr, it can crush any structure it meets. It ranges in size from an ash particle, all the way to boulders and the heat can range from 200 C to 700 C.
---------- Pyroclastic flows erupted by Mount Pinatubo on June 15, 1991, buried the Marella River valley. The depth of the ash fallout was between 50 and 200 m. The pyroclastic flows traveled as far as 12 to 16 km from the volcano in all directions.
--------- A small pyroclastic flow traveled down the narrow Belham stream channel as far as 5 to 6 km from Soufriere Hills volcano in Montserrat. The hot ash cloud burned and killed all vegetation along the channel.
Lava flow are streams or rivers of red, hot molten rock. They slowly move their way down slopes, until they finally reach ocean or sea levels. Lava flows are a major threat, but usually move fairly slow, so they are not a major source of death, although they do create major destruction economically. Everything in a lava flows path will be knocked over, burned or ignited by the extremely hot lava.
-----------`A`a lava flow moves through an intersection in the Royal
Garderns subdivision on the south flank of Kilauea Volcano, Hawaii.
-------- Two cauldrons above an erupting fissure beneath the Vatnajökull glacier, located in Central Iceland.
Mud Flows (Lahar) -
One of the greatest volcanic hazards is a lahar.
They are very much like pyroclastic flows. However, they are mainly consisting of water and small sediment. Lahars happen when volcanoes erupt and the ice caps on top of the volcano melt due to extreme heat.
Also lava flow from a previous eruption can create a dam, which in time creates a lake and then in time another eruption takes place and releasing the water and floods mountain sides etc.
------------ Dark pathways created by lahars streak the sides of Mount St.
Helens during its eruption on May 18, 1980. The lahars were triggered by the sudden melting of snow and ice from hot volcanic rocks ejected by the initial explosive activity and subsequent pyroclastic flows
----------- Number and type of volcanic events known to have generated lahars by melting snow and ice during historical eruptions. This 1989 study was based on 108 historical eruptions from around the world.
Volcanic Landslides –
Landslides are huge amounts of soil that are released from the mountainside, due to the gravity and earthquakes. Like an avalanche and a pyroclastic flow or dry lahars. When these take place, they will run over and crush anything in its path.
------Start of landslide
------Landslide enters valley
Tsunami’s are the most destructive waves in the ocean. Most people have mistaken them for tidal waves. Many different things cause them: Impacts in the water, landslides, earthquakes and etc.
The ring of fire underneath the Pacific Ocean creates four to five tsunami’s a year. Luckily we as Canadians, on the East coast, have to experience such
horrible devastation yet.
--------------Tsunami crashes in to an old city, Europe 1600’s.