 Magma chamber is where magma collects in a
pocket.
 Pipe is the long tube connecting the magma
chamber to the Earth’s surface.
 Vent is the opening for the molten rock and gas to
escape.
 The lava flow is the area covered by lava as it flows
out of the vent.
 A crater is a bowl-shaped area that may form at the
top of volcano around the central vent.
 Key point – When a volcano erupts, the force of the
expanding gases pushes magma from the magma
chamber through the pipe until it flows or explodes
out of the vent.
 Quiet eruptions
 Explosive eruptions
 Volcano hazards
 Magma is low in silica
 Low silica magma is thin and runny
 Flows easily
 Gases in magma bubble out gently.
 Two different lava’s are produced.
 Pahoehoe (ropelike and wrinkly)
 This lava thin and runny.
 Aa is thicker than Pahoehoe.
 Lava is cooler and slow moving
 As aa hardens, it forms a rough surface consisting
of jagged lava chunks.
 Magma is high in silica.
 Magma is thick and sticky
 Volcano’s pipe becomes plugged with gooey mess.
 Pressure builds as gases try to escape.
 A powerful explosion follows.
 Many types of sizes of lava fragments occur from
this explosion.
 Volcanic ash – almost dust like.
 Cinders – pebble-sized particles
 Bombs – size of baseball to size of a car
 A pyroclastic flow hurls out mixture of hot gases,
ash, cinders, and bombs.
 A quiet eruption can send lava flowing and
destroying everything in its path.
 In a explosive eruption , ash can bury entire towns
and collapse roofs.
 Eruptions can cause landslides and avalanches of
mud, melted snow, and rock.
 Activity of volcanoes can last from a decade to more
than 10 million years.
 Active – the volcano is either erupting or about to
erupt.
 Dormant – Sometime in the future this volcano will
awaken and erupt again.
 Extinct – This volcano will likely never erupt again.
 Found in areas of present or past volcanic activity.
 Hot springs occur when deep underground water is
heated by magma or hot rock.
 The hot water rises to the top and collects in a
natural pool.
 Hot water that gets trapped in a narrow crack will
eventually build up pressure and erupt causing a
geyser at the surface.
 Geologists use instruments to detect changes in and
around a volcano.
 Tiltmeters are used to measure slight surface
changes in elevation and tilt caused by magma
moving underground.
 Instruments are used to measure gases escaping
from a volcano.
 Temperature increase can be a sign that magma is
getting closer to the surface.
 Small earthquakes are monitored because it could
be a sign that magma is coming closer to the
surface.