Ash Clouds and Airplanes

1
Ash Clouds and Airplanes
http//pubs.usgs.gov/pinatubo/casa/

• Aviation hazard
• gt80 aircraft have unexpectedly encountered
  volcanic ash in flight and on ground
• Seven caused in-flight loss of jet engine power,
  which nearly resulted in crash of the airplane
• Types of damage
• Reduces engine performance May cause failure
• Abrades components
• Forms glassy coating which covers cooling
  passages
• Abrades external components, leading edges,
  windshields, etc.
• Contaminates interior

2
Volcanic Gases
Poisonous Gas Emissions

• Gases released CO2, SO2, H2S, CO, H2, NH3, CH4
  and some others
• Formation of acid rain (from SO2) can cause water
  contamination and plant damage
• Prevailing winds can blow gases thousands of
  kilometers away

3
Lake Nyos, Africa, 1986 large amount of carbon
dioxide expelled from lake floor sediments. Gas
traveled down the mountain, into 5 villages and
killed gt 1700 people in their sleep
http//volcanoes.usgs.gov/Hazards/What/VolGas/volg
as.html
4
Lahars (Mudflows)
Secondary Effects of Volcanism
Mudflow Hazard Potential

• Rapidly flowing mixture of rock debris and water
• Can travel 10s of kms,
• typically down river valleys
• Especially common at stratovolcanoes
• Generated
• Without eruptions
• Landslides mixed with water
• During eruptions
• Melting of snow and ice by pyroclastic flows,
  lava flows
• After eruptions
• Heavy rainfall erodes deposited ash, etc.
• Sudden release of water from crater lakes

Fig. 3.23, page 84, Natural Hazards
5
Definition of an active, dormant and extinct
volcano

• Active Volcano - An active volcano to a scientist
  is a volcano that has shown eruptive activity
  within recorded history.
• It's important to note that the span of recorded
  history differs from region to region in the
  Mediterranean, recorded history reaches back more
  than 3,000 years but in the Pacific Northwest of
  the United States, it reaches back less than 300
  years, and in Hawaii, little more than 200 years.
• Currently there are about 600 volcanoes on Earth
  considered to be active volcanoes.
• Each year 50 to 60 of volcanoes actually erupt.

6
Extinct Volcano - An extinct volcano is a volcano
that has not shown any historic activity, is
usually deeply eroded, and shows no signs of
recent activity. How old must a volcano be to be
considered extinct depends to a large degree on
past activity. Dormant Volcano - A dormant
volcano (sleeping volcano) is somewhere between
active and extinct. A dormant volcano is one that
has not shown eruptive activity within recorded
history, but shows geologic evidence of activity
within the geologic recent past. These are
perhaps the most dangerous volcanoes because
people living in the vicinity of a dormant
volcano may not understand the concept of
geologic time, and there is no written record of
activity. These people are sometimes difficult to
convince when a dormant volcano shows signs of
renewed activity.
7
Minimizing the volcanic hazard - Forecasting

• Monitoring seismic activity
• Increased earthquake activity may be precursor
  for a volcanic eruption
• Heat discharge/Water flows
• Changes in temperature, water table depth.
• Increased temperatures at surface of volcano due
  to rising magma.
• Monitoring the land surface to detect tilting
• Rising magma chamber may cause land surface to
  tilt

Volcanologists capture gases emitted from vents,
fumaroles, lakes and soil.

• Monitoring gas discharge
• Changes in gas emission rates, such as hydrogen
  chloride and sulfur oxide may indicate rising
  magma.
• Studying the geologic history of a volcano

8
Volcanic Hazard Mitigation Adjustments to the
volcanic hazard
Mitigation activities, processes or procedures
designed to reduce and/or eliminate the threats
of volcanic hazards
Explosive Diversion use of explosives to
either create channels or barriers in the path of
advancing lava, or to breach levees in order to
divert the flow
Lahar Diversion Sabo Dams dams constructed in
river valleys, designed to strain out large
debris divert lahar away from people/property
minimize erosion common in Japan and Indonesia
where large populations live and work near/in the
threatened river valleys
9
Water Cooling rapid cooling of the flow front
using cold water in order to strengthen the lava
and form a natural blockage used in Iceland in
1973 to try to stop a flow from closing off and
important harbor used north Atlantic seawater
for days many scientists are convinced that the
flow was stopping and that the water did very
little
Cost 1,447,742 U.S A total of 6.2 million
metric tonnes of seawater was pumped in all.
10
Public Education can be critical in reduction
of the risks needed in third world countries
where the population is high and the information
dissemination is low needed also in first
world countries where the recurrence interval is
large and therefore the perceived threat from
volcanoes is minimal

• begin training early (Japan does this for grade
  school kids living in hazard-prone areas)
• continue public education/drills/training in
  those areas (especially before and during a
  hazard)
• increase funding for monitoring at hazardous
  volcanoes
• eventually produce a geologic and hazards map
  for the volcano and the surrounding areas

11
Geographic areas at risk Stratovolcanoes are
associated with subduction zones Most common type
along the ring of fire Example Volcanoes of the
Cascade Range of Washington, Oregon and
California are derived from the Cascadia
subduction zone This area experiences the highest
risk of local volcanic activity in the States.
Mid-ocean ridges produce basaltic lava of very
low viscosity basalt therefore producing shield
volcanoes
12
Casita Volcano1998 Landslide and Lahar
Nicaragua

• The side if Casita volcano (inactive) collapsed
  on October 30, 1998
• Day of peak rainfall as Hurricane Mitch moved
  across Central America
• Increased in size (9 times) as older deposits
  eroded additional water incorporated
• 2,000 fatalities
• One of many towns so close to volcanoes that
  lahar warning systems ineffective
• Only 2.5-3 minutes warning
• No quickly assessable high ground
• Solution Keep settlements out of (pre)historic
  lahar pathways

All from http//volcanoes.usgs.gov/Hazards/What/La
hars/CasitaLahar.html