Subpart E 
OTHER
NATURAL HAZARDS

216 NATURAL HAZARDS

Introduction
V
olcanoes and wildfires are among 
the most frightening natural hazards 
and pose significant threats to people, 
property, and wildlife. 
The United States has more than 65 potentially 
active volcanoes, with the greatest 
activity in the Western States, Alaska, and 
Hawaii. Nonexplosive and explosive volcanoes 
produce debris flows and avalanches, 
pyroclastic flows and surges, floods, lava 
flows and domes, volcanic ashfalls and 
gases, and lateral blasts. Lava flows tend to 
follow historic paths, simplifying identification 
of areas at greatest risk. Ashfall can 
spread well beyond the immediate eruption 
area. Volcanic activity often causes other 
hazardous events, such as landslides and 
wildfires. 
Wildfires occur in virtually every State, 
however, more frequent incidents occur in 
the Western States, particularly California. 
Four types of wildfires constitute the hazard: 
wildland fires, interface or intermix fires, 
firestorms, and prescribed fires. Wildfires 
often are ignited by lightning. The severity 
of an event can be influenced by other natural 
hazards, such as drought and windstorms. 
As more people move into the forest inter-
face and wildland settings, exposure to this 
hazard increases. 
Photo: FEMA 



220 NATURAL HAZARDS: OTHER NATURAL HAZARDS
Chapter Summary
H
azards associated with the eruption of volcanoes 
endanger people, buildings, and infrastructure. 
Nonexplosive and explosive eruptions produce 
debris flows and avalanches, pyroclastic flows and surges, 
floods, lava flows and domes, ashfalls and gases, and lateral 
blasts. Areas at risk from volcanic eruptions primarily 
are those in or near the direct path of flows, although 
ashfalls affect people, the environment, and aircraft for 
extended distances. 
In the 1980s, volcanoes worldwide killed over 28,500 people, 
more than during the first 80 years of this century 
(Wright and Pierson, 1992). This decade experienced 
more worldwide volcanic activity and crises than any other 
in recorded history (Lipman and Mullineaux, 1981). The 
cataclysmic Mount St. Helens eruption in 1980 resulted in 
approximately 60 deaths and over $1.5 billion in damage. 
Other volcanic activity during the 1980s included Mauna 
Loa and Kilauea in Hawaii, Long Valley Caldera in 
California, and Redoubt in Alaska. 
More than 65 active or potentially active volcanoes exist in 
the United States, more than all other countries except 
Indonesia and Japan. Most are located in Alaska, and 55, 
including eight on the mainland, have been active since the 
United States was founded (Simkin and others, 1981). 
Following the eruption of Redoubt in 1989, scientists monitored 
the volcano using ground and seismic signal amplitude 
measurements, slow-scan video photography, and 
lightning and debris-flow detection systems. Use of these 
technologies will enhance detection and warning. Disaster 
preparedness and evacuation planning may reduce injuries 
and loss of life. Identification of hazard zones for land-use 
planning may help address property damage. 

Photo: Keith Ronnholm, FEMA 

222 NATURAL HAZARDS: OTHER NATURAL HAZARDS
HAZARD IDENTIFICATION 
Eruptions of U.S. volcanoes can generate serious hazards, 
any of which can be deadly (Wright and Pierson, 
1992): 
 Glowing rivers of molten rock or lava flows; 
 Devastating shock waves and fiery blasts of debris 
from volcanic explosions, called pyroclastic surges; 
 Red-hot avalanches of rock fragments racing down 
mountainsides, called pyroclastic flows; and 
 Suffocating blankets of volcanic ash falling from the 
sky. 
Volcanic eruptions are classified as nonexplosive or 
explosive. Nonexplosive eruptions generally are 
caused by an iron- and magnesium-rich magma (molten 
rock) that is relatively fluid and allows gas to escape 
readily. Lava flows on the Island of Hawaii are typically 
of nonexplosive eruptions. 
In contrast, explosive eruptions are violent and are 
derived from a silica-rich magma that is not very fluid. 
These eruptions are common in the Cascade Range 
(Washington, Oregon, and California) and in the volcanic 
chain of Alaska. Explosive eruptions produce 
large amounts of fragmental debris in the form of air-
borne ash, pyroclastic flows and surges, debris flows, 
and other hazards on and beyond the flanks of the volcano, 
endangering people, infrastructure, and buildings 
(Hays, 1981). 
Lava Flows. Lava flows are streams of molten rock 
that erupt relatively nonexplosively and move downs-
lope. The distance traveled by a lava flow depends on 
such variables as viscosity, volume, slope steepness, 
and obstructions in the flow path. Lava flows typically 
extend from 6 to 30 mi (10 to 50 km). 
Lava flows cause extensive damage or total destruction 
by burning, crushing, or burying everything in their 
paths. They need not directly threaten people, however, 
because they usually move slowly (a few feet to a 
few hundred feet per hour) and their paths can be 
roughly predicted. Lava flows that move onto snow 
and ice can cause destructive debris flows and floods, 
and those that move into forests can cause wildfires. 
The flanks of lava flows typically are unstable and collapse 
repeatedly, occasionally producing explosive 
blasts and small pyroclastic flows. 
Pyroclastic Flows. Pyroclastic flows are high-
density mixtures of hot, dry rock fragments and hot 
gases that move away from source vents at speeds of 30 
to +90 mph (48 to +145 km/h), extending dozens of 
miles. They can result from explosive lateral eruptions 
of molten or solid rock fragments, from the collapse of 
vertical eruption columns of ash and larger rock fragments, 
or from the fall of hot rock debris from the surface 
of a dome or thick lava flow. Rock fragments in 
pyroclastic flows range widely in size and consist mostly 
of dense debris or pumice fragments (Hoblitt and 
others, 1987; Miller, 1989). 
Pyroclastic flows are extremely hazardous because of 
rapid movement and very high temperatures. Objects 
and structures are destroyed or swept away by the 
impact of debris or associated hurricane-force winds. 
Wood and other combustible materials are burned, and 
people and animals may be burned or killed by contact 
with hot debris and gases. 
Pyroclastic Surges. Pyroclastic surges are turbulent, 
low-density clouds of rock debris, air, and other 
gases that move over the ground surface at speeds similar 
to pyroclastic flows. Pyroclastic surges can be of 
two types: hot surges that consist of dry materials that 
have temperatures appreciably above 212F (100C); 
and cold surges that consist of cooler rock debris and 
steam or water. Both types can extend as far as 6 mi (10 
km) from source vents and devastate life and property 
in their paths (Miller, 1989). 
Lava Domes. Lava domes are masses of solid rock 
that are formed when viscous lava erupts slowly from a 
vent. If the lava is sufficiently viscous, it will pile up 
above the vent to form a dome rather than move away 
as a flow. The sides of most domes are very steep and 
typically are mantled with unstable rock debris formed 
by cooling during or shortly after dome formation. 
Most domes are composed of silica-rich lavas that have 
a lower gas content than do the lavas that erupted earlier 
in the same eruptive sequence. Nevertheless, some 
dome lavas contain enough gas to cause explosions during 
formation. The direct effects of dome eruption 
include local burial or disruption of the preexisting 
ground surface by the dome itself, and widespread burial 
by rock debris if part of the dome collapses. 
Because of high temperatures, lava domes may start 
fires if they erupt into forests. Domes are extruded so 
slowly that they can be avoided by people and animals, 
but structures are endangered. The major hazard is 
pyroclastic flows that can occur without warning and 
move very rapidly, endangering life and property for 
distances up to 12 mi (20 km) from the source. 

Volcanic Ash. Volcanic ash, called tephra, is composed 
of fragments of lava or rock blasted into the air by 
explosion or carried upward by a rising column of hot 
gases to form an ash plume. Fragments fall back to 
earth forming ash deposits, which blanket the ground 
with a layer that decreases in thickness and particle size 
away from the source. 
Ash-producing eruptions range from short-lived weak 
ones that eject debris only a few feet into the air to cataclysmic 
explosions that throw debris dozens of miles 
into the atmosphere. Explosive eruptions that produce 
voluminous ash deposits commonly produce pyroclastic 
flows. 
Close to an erupting vent, the main hazards to property 
posed by volcanic ash include high temperatures, burial, 
and impact of falling fragments. Large, falling blocks 
can kill or injure exposed people and animals. 
Significant property damage can result from the weight 
of volcanic ash, especially if it is wet: 8 in (20 cm) or 
more of ash depth may cause structures to collapse. Hot 
ash may set fire to forests and buildings. 
Farther away from a vent, the chief danger to life is the 
effect of ash on respiratory systems. Even 2 in (5 cm) 
of volcanic ash will mechanically impair most vehicles 
and disrupt transportation, communication, and utility 
systems. Machinery is especially susceptible to the 
abrasive and corrosive effects of volcanic ash. These 
effects, together with decreased visibility or darkness 
during an eruption, may further disrupt normal services, 
and may cause psychological stress and panic among 
people whose lives may otherwise not be endangered. 
Volcanic Gases. Volcanic gases consist predominately 
of steam, followed in abundance by carbon dioxide 
and compounds of sulfur and chlorine. Minor 
amounts of carbon monoxide, fluorine and boron compounds, 
ammonia, and several other compounds are 
found in some volcanic gases. 
Distribution of volcanic gases is controlled primarily by 
wind. Gases may be concentrated near a vent, but 
become rapidly diluted downwind. However, even very 
dilute gases can have noticeable odors and can harm 
plants and some animals dozens of miles downwind 
from a vent. 
Close to a vent, volcanic gases can endanger people's 
lives and health as well as property. Acids and ammonia 
and other compounds present in volcanic gases can 
damage eyes and respiratory systems of people and animals. 
Accumulations of gases heavier than air, like car-
bon dioxide, can lead to suffocation. Other harmful 
effects of volcanic gases and corrosion of metals and 
other property can be severe near and downwind from 
very active vents. 
Lateral Blasts. Lateral blasts are inflated mixtures 
of hot rock debris, ash, and gases and may be hundreds 
of feet thick and move at high speeds along the ground 
surface with little or no influence by the underlying 
topography. Blasts are known to reach speeds up to 370 
mph (595 km/h). Lateral blasts can produce pyroclastic 
flows or surges or both (Hoblitt and others, 1987). 
Lateral blasts are among the most destructive of volcanic 
phenomena. Within minutes, they can devastate 
hundreds of square miles and kill virtually all living 
things in their wake by abrasion, impact, burial, and heat 
(Miller, 1989). A lateral blast at Mount St. Helens in 
1980 devastated an area of 230 mi2 (596 km2), extending 
as much as 17 mi (27 km) from the volcano and 
killing more than 60 people. 
Debris Avalanches. A debris avalanche is a sudden 
and very rapid movement of an incoherent and 
unsorted, wet or dry mixture of rock and soil that is 
mobilized by gravity. Debris avalanches commonly 
originate in massive rock slides which, during movement, 
disintegrate into fragments ranging from small 
particles to blocks hundreds of feet across. Debris 
avalanches occur occasionally on large, steep-sided volcanoes 
and are among the most hazardous of volcanic 
events (Voight and others, 1981; Crandell, 1984). 
Deposits from volcanic debris avalanches can extend for 
dozens of miles and cover as much as 300 mi2 (777 
km2). The debris avalanche and landslide associated 
with the May 18, 1980, eruption of Mount St. Helens 
deposited 0.7 mi3 (2.8 km3) of poorly sorted debris to an 
average depth of 150 ft (45 m) over approximately 25 
mi2 (60 km2) of the North Fork Toutle River Valley. The 
level of Spirit Lake was raised approximately 200 ft (60 
m) (Lipman and Mullineaux, 1981). 
Debris avalanches can destroy everything in their path 
by direct impact or by burial beneath dozens of feet of 
debris. Because debris avalanches can occur with little 
or no warning and can travel at high speeds (Voight and 
others, 1981), areas that might be affected should be 
evacuated if an avalanche is anticipated. 
Debris Flows. Debris flows are mixtures of water-
saturated rock debris that flow downslope under the 
force of gravity. They are sometimes called mudflows 
or "lahars," an Indonesian word. Debris flows consist of 
material varying in size from clay particles to blocks 
several dozens of feet in dimension. When moving, 
they resemble masses of wet concrete and tend to flow 
along channels or stream valleys. Debris flows are 

224 NATURAL HAZARDS: OTHER NATURAL HAZARDS
formed when loose masses of unconsolidated debris 
become unstable due to wetting by rainfall, melting 
snow or ice, or by overflow of a crater lake. 
Debris flows can travel great distances down valleys, 
and debris-flow fronts can move at speeds up to 60 mph 
(97 km/h). The debris flows that descended the south-
east flank of Mount St. Helens in 1980 had initial flow 
velocities that exceeded 60 mph (97 km/h). Average 
flow velocities were approximately 40 mph (64 km/h) 
over the 14 mi (23 km) distance traveled before the 
flows entered a reservoir (Pierson, 1985). 
The primary danger posed by debris flows to people is 
from burial or impact of boulders and other debris. 
People and animals can be severely burned by hot 
debris flows. Buildings and other property in the path 
of a flow can be buried, smashed, or carried away. 
Because of their relatively high density and viscosity, 
debris flows can move and even carry away vehicles 
and objects as large as bridges and locomotives (Miller, 
1989). 
Floods. Floods and hyperconcentrated flows can 
result from melting of snow and ice during eruptions, 
heavy rains that often accompany eruptions, and by 
transformation of debris flows to streamflows. 
Hyperconcentrated flow originally was defined by 
Beverage and Culbertson (1964) as streamflow with 
sediment concentrations between 40 and 80 percent by 
weight (20 and 60 percent by volume). 
The sequence of flow events is from debris avalanche to 
debris flow to hyperconcentrated flow to flood, as the 
coarser materials come to rest and the water content 
increases. Pierson and Costa (1987) provide additional 
details on the classification of flows. 
Floods carrying unusually large amounts of rock debris 
and sediment can leave thick deposits of sand and gravel 
at and beyond the mouths of canyons and on valley 
floors leading away from volcanoes. Eruption-caused 
floods can occur suddenly and can be large in volume if 
rivers are already high because of heavy rainfall or 
snowmelt. Floods also can be generated by eruption-
caused seiches (waves) that overtop dams or move 
down outlet streams from lakes. 
RISK ASSESSMENT 
Probability and Frequency 
An inverse relation exists between the size of the eruptions 
(volume of material erupted) and how often they 
occur. Small eruptions occur much more frequently 
than large ones. The volumes and frequencies of past 
eruptions provide the major criteria for defining hazard 
zones. 
Newhall (1984) describes a procedure for quantifying 
the short-term (week-to-week or shorter), intermediate 
(month-to-month) and long-term (year-to-year) frequency 
of volcanic eruptions. Newhall's conditional 
probability analysis is very detailed and has not been 
applied to all U.S. volcanoes. One simplified approach 
to estimate the annual probability of exceedance is to 
divide the number of known explosive eruptions by the 
duration of the eruptive record (Mullineaux, 1976; 
Hoblitt and others, 1987). The annual probability of 
exceedance or frequency of active and potentially 
active volcanoes can be estimated from historical 
records which are summarized in Table 18-1 (Wright 
and Pierson, 1992). 
TABLE 18-1.Selected active and potentially active U.S. volcanoes. 
Volcano Eruption 
Type(s) 
Eruptions 
in Past 200 
Years 
Last 
Active 
Remarks 
Kilauea, HI Lava, most 
common; 
ash, rare 
47 Ongoing from 
1983 
Explosive eruption at Kilauea summit in 1790 killed 
approximately 80 Hawaiian warriors. Eruptions 
presenting lava-flow hazard to coastal areas: four in 
the 19th century; five in the 20th century. 
Mauna Loa, HI Lava 30 1984 Eruptions presenting lava-flow hazard to coastal areas; 
eight in the 19th century; eight in the 20th century. 
Hualalai, HI Lava, ash 1 1800-1801 High hazard due to unusually fluid lava. 
Mount Baker, WA Ash, lava 1? 1870 Increased heat output and minor melting of summit 
glacier in 1975; some debris flows not related to 
eruption. History of extensive pyroclastic flows. 
Mount Rainier, WA Ash, lava 1? 1882 (?) History of massive debris avalanches and debris flows. 
Occasional very shallow seismicity. 

TABLE 18-1.Selected active and potentially active U.S. volcanoes. (continued) 
Volcano Eruption 
Type(s) 
Eruptions 
in Past 200 
Years 
Last 
Active 
Remarks 
Mount St. Helens, 
WA 
Ash, dome, 
lava 
2-3 1980 - present Continuing intermittent volcanic activity. 
Mount Jefferson, 
OR 
Ash, lava 0 More than 
50,000 years 
ago 
Debris flows in 1934, 1955; young basaltic flows in 
nearby area. 
Three Sisters, OR Ash, lava 0 950? Debris flows in this century. 
Crater Lake, OR Ash, lava, 
dome 
0 4,000 years 
ago 
Largest known eruption from Cascade Range volcano. 
Catastrophic, caldera-forming eruption 7,000 years 
ago; post-caldera lava and domes. 
Mount Shasta, CA Ash, dome 1 1786? Debris flows in this century. 
Lassen Peak, CA Ash, dome 1 1914 - 1917 Lateral blast occurred in last eruption. 
Clear Lake, CA Lava, ash 0 Not known Geothermal energy and long-period (volcanic) 
seismicity suggest active status. 
Long Valley 
Caldera, CA 
Ash, dome, 
ashflow 
3? About 1400 Youngest activity represented by nearly simultaneous 
eruptions of rhyolite at several of the Inyo craters; 
currently restless, shown by seismicity and ground 
deformation. 
San Francisco 
Field, AZ 
Lava 2 1065-1180 Sunset Crater; disrupted Anasazi settlements. 
Bandera Field 
(McCartys 
Flow), NM 
Lava 1 About 1000 Most voluminous lava within past 1,000 years. 
Craters of the 
Moon, ID 
Lava About 1 2,100 years 
ago 
Youngest activity in the Snake River Plain. 
Yellowstone 
Caldera, WY, 
MT, ID 
Ashflow 0 70,000 years 
ago 
Numerous hydrothermal explosions, geysers, 
geothermal activity; currently restless, shown by 
seismicity and ground deformation. 
Wrangell, AK Ash 1? 1902? Emission of gases and vapors from vents (fumarolic 
activity). 
Redoubt Volcano, 
AK 
Ash, dome 4 Ongoing Eruption began December 1989. 
Mount Emmons 
Pavlof Volcano, AK 
Ash, lava 30 1987 Pavlof is most frequently active volcano in Alaska. 
Kiska Volcano, AK Ash, lava 7 1990 Steam and ash emission. 
Pyre Peak 
(Seguam), AK 
Ash, lava 5 1977 Eight lava fountains, as high as 90 meters. 
Mount Cleveland, 
AK 
Ash, lava 10 1987 1945 eruption resulted in only known fatality from 
Alaska volcanism. 
Source: Wright and Pierson, 1992. 

226 NATURAL HAZARDS: OTHER NATURAL HAZARDS
Exposure 
With the exception of ashfalls, the areas at risk from 
volcanic eruptions primarily are those in or near the 
direct paths or channels of flowing material and debris. 
Thus, beyond the flanks of volcanoes, the most hazardous 
areas are the floors of valleys that head on volcanoes. 
Risks associated with volcanic hazards 
decrease as distance increases. 
Western Conterminous United States. 
Mullineaux (1976) defined hazard zones for volcanoes 
in the Western States based on three categories: ashfall, 
lava flows, and other flow phenomena such as avalanches, 
debris flows, or floods. The major categories of hazards 
were described in terms of origin and characteristics, 
location, size of area affected by a single event, 
general effects, areas endangered by future eruptions, 
frequency in the conterminous United States as a whole, 
and degree of risk in affected areas. 
Areas of the conterminous United States affected by 
volcanic hazards are shown on Map 18-1, adapted from 
Mullineaux (1976). Hazard zone boundaries are only 
approximate and the degree of hazard varies gradually 
from one zone to the next. The darkest areas shown are 
subject to lava flows and/or 2 inches or more of ashfall 
and include groups of volcanic vents termed volcanic 
fields, where future eruptions chiefly of lava flows and 
moderate volumes of ash are more likely than in nearby 
areas. 
Areas subject to 2 in (5 cm) or more of ashfall from a 
large eruption that would occur once every 1,000 to 
5,000 years (0.10 to 0.02 percent annual chance of 
exceedance) are the medium shaded regions. Finally, 
those areas subject to 2 in (5 cm) or more of ashfall from 
a very large eruption that would occur about once every 
5,000 to 10,000 years (0.02 to 0.01 percent annual 
chance of exceedance) are shown lightly shaded. 
Hoblitt and others (1987) provide a detailed analysis of 
hazards from 13 major volcanoes in the Cascade Range 
in the Western States, identifying areas subject to directed 
blasts, pyroclastic flows and surges, debris avalanches, 
lava flows, debris flows and floods, and accumulations 
of ashfall. 
Hawaii. There are seven active or potentially active 
volcanoes in Hawaii. Six are on or just offshore of the 
Island of Hawaii. Kilauea and Mauna Loa have erupted 
47 and 30 times, respectively, during the last 200 
years, making them two of the most active volcanoes in 
the world. Kilauea has erupted continuously since 
1983. The Haleakala volcano is located on Maui. 
Lava flows are the most common direct volcanic hazard 
in Hawaii. Using data on the location and frequency of 
historic and prehistoric eruptions, Heliker (1990) developed 
a lava flow hazard zone map for the Island of 
Hawaii (Table 18-2). 
Alaska. Most of the active or potentially active volcanoes 
in the United States are in a chain of volcanoes 
that extends 1,550 mi (2,500 km) from near Anchorage 
southwest along the Alaskan Peninsula to the western 
Aleutian Islands (Map 18-2). On average, at least one 
lcano in the chain erupts each year (Simkin and others, 
1981). In 1912, Novarupta produced the largest eruption 
of the 20th century (Wright and Pierson, 1992). 
Scientists have identified more than 40 historically 
active volcanic centers along the chain. Eruptions could 
affect the Cook Inlet region, where 60 percent of 
Alaska's population resides and which is the State's 
major supply, business, and financial center (Brantley, 
1990). 
Consequences 
Western Conterminous United States. 
Mount St. Helens, WA, erupted explosively in 1980, 
preceded by more than 10,000 local earthquakes and 
hundreds of steam blasts. Timber worth several million 
dollars was destroyed in a 596 km2 (230 mi2) area. Over 
290 tons of ash were spread across 57,000 km2 (22,000 
mi2) and extended as far east as North Dakota. 
Landslides along the volcano's flanks traveled about 14 
mi (22.5 km) and mudflows destroyed bridges, temporarily 
halted shipping on the Columbia River, and disrupted 
highways and rail lines. Nearly 60 people were 
killed, and total costs exceeded $1.5 billion. 
Despite no significant activity in the past 500 years, Mt. 
Rainier, WA, is considered to be the most hazardous 
volcano in the Cascades, primarily due to the threat of 
mudflows and floods. Twenty-six glaciers on the volcano 
contain large volumes of water that could be melted 
during active periods. 
In western central California, the caldera known as 
Long Valley-Mono Lake was revealed to have some 
activity when an upward bulge of nearly 25 cm (10 in) 
was discovered during a 1980 survey of U.S. Route 395. 
The bulge is thought to be due to accumulations of rising 
magma. Geologic evidence of extensive ashfall 
from Long Valley has been found more than 1,000 km 
(600 mi) east and south of the site, covering all of 
Southern California, the entire States of Utah, Arizona, 
Colorado, and significant portions of New Mexico, 
Wyoming, Nebraska, and Kansas. 

Map 18-1Map 18-1. Areas subject to lava flows and ashfall in the conterminous United States. 
Data not available for Alaska, Hawaii, Puerto Rico, U.S. Virgin Islands, and Pacific Territories. 
Source: Data from Mullineaux, 1976. 

228 NATURAL HAZARDS: OTHER NATURAL HAZARDS
Hawaii. Kilauea on the Island of Hawaii has been 
active since the early 1980s. By June 1991, the shield 
was over 60 m (37 ft) tall, had covered 78 km2 (30 mi2) 
of forest and grassland, and had destroyed 180 homes 
and closed highways. Land values in the area dropped 
rapidly, and some insurance companies refused to sell 
new policies. During the period 1984-86, fumes 
released from Pu'u O'o vent 12 mi (19 km) from the 
summit damaged crops. In 1790, Kilauea erupted with 
pyroclastic surges and ash fell 30 km (18.5 mi) from the 
summit. Suffocating gas killed many people. 
Mauna Loa, the largest volcano on the Island of Hawaii, 
has erupted 15 times since 1900. Events lasted from 1 
to 145 days. In 1984, the three-week long lava flow 
came within 6.5 km (4 mi) of buildings in the City of 
Hilo. 
Alaska. Although sparsely populated, violent eruptions 
could threaten Alaskas towns and villages. At 
least one or two eruptions have occurred each year 
since 1900 (Brantley, 1994). 
Ash is the most common and widespread volcanic hazard 
in Alaska, and is especially dangerous to aircraft 
(Brantley, 1990). At least four commercial jet aircraft 
suffered damage during the 1989-90 eruption of 
Redoubt Volcano. Ash generated by numerous explosive 
episodes caused significant damage to aircraft, 
severely disrupted air traffic above southern Alaska, 
and resulted in local power outages and school closings. 
The explosions produced hot, fast-moving clouds of 
ash, rock debris, and gas (pyroclastic flows) that swept 
across Redoubt's heavily glaciated north flank. 
The most serious incident occurred on December 15, 
1989, when a Boeing 747 jetliner carrying 231 passengers 
entered an ash cloud approximately 150 mi (240 
km) northeast of Redoubt Volcano. The jet lost power 
in all four engines and dropped approximately 13,000 ft 
(4,000 m) before the pilot succeeded in restarting the 
engines. The plane landed safely in Anchorage, but 
sustained an estimated $80 million in damage 
(Steenblik, 1990). This near-tragic incident prompted 
government agencies to search for better ways to track 
ash plumes and to improve information for the airline 
industry. 
The Redoubt eruption triggered massive debris flows in 
Drift River Valley, threatening an oil tanker terminal 
near the river's mouth. On two occasions, partial flooding 
of the terminal compound forced authorities to 
modify operating procedures which temporarily cur-
tailed oil production from 10 platforms in Cook Inlet. 
The damage and loss of revenue from ash and debris 
TABLE 18-2.Lava flow hazard zones for the Island of Hawaii 
Hazard 
Zone 
Percent of Area 
Covered by Lava 
Since 1800 
Percent of Area 
Covered by Lava 
in Last 750 Years 
Explanation 
Very high >25 percent >65 percent Kilauea and Mauna Loa 
rift zones where vents 
have been very active in 
historic time. 
High 15-25 percent 25-75 percent Areas adjacent to and 
downslope of active rift 
zones. 
Moderately high 1-5 percent 15-75 percent Areas less because of 
greater distance from 
active vents or areas 
protected by topography. 
Moderate About 5 
percent 
<15 percent Includes all of Hualalai, 
where frequency of 
eruptions is less than 
Kilauea and Mauna Loa. 
Low None Very Little Areas currently protected 
by topography or no 
eruptions in recorded 
history. 
Source: Modified from Heliker, 1990. 

Figure 18-1FIGURE 18-1.Volcanoes of the Aleutian Arc. 
Source: Motyka, and others, 1993. 
flows was estimated at more than $100 million, the second 
most costly eruption in the history of the United 
States. 
RESEARCH, MONITORING, AND DATA 
COLLECTION ACTIVITIES 
The seismicity associated with earthquakes often provides 
the earliest warning of volcanic unrest, as earth-
quake swarms immediately precede most eruptions. 
Geodetic networks are set up to measure changes in 
volcano surface caused by the pressure of moving 
magma. Changes in the gas composition, or in the 
emission of sulfur dioxide and other gases, may be 
related to variation in magma supply rate, changes in 
magma type, or modifications in the pathways of gas 
escape induced by magma movement. Changes in electrical 
conductivity and magnetic field strength also 
trace magma movement. Changes in groundwater temperature 
or levels, rates of streamflow and sediment 
transport, and changes in lake levels, snow, and ice 
accumulation may be indicative of impending volcanic 
activity. 
State-of-the-art technology was used to monitor the 
1989 eruption of Redoubt Volcano. These techniques 
can improve detection and monitoring to enhance warning 
capabilities that lead to reduction of losses 
(Brantley, 1990): 
 Real-Time Seismic Amplitude 
Measurement (RSAM). Unlike other seismic 
data acquisition systems that continuously record the 
oscillation of the ground, RSAM computes and stores 
the average amplitude of ground oscillation over 10-
minute intervals. As either the magnitude or number 
of earthquakes increases, and as volcanic tremors 
increase, the average amplitude of ground oscillation 
also increases. The advantage of the RSAM system 
is its ability to measure the level of seismicity during 
intense activity, especially during eruptions and volcanic 
tremor, and when earthquakes are so numerous 
that individual events cannot normally be distinguished 
and counted. 
 Seismic Spectral Amplitude 
Measurement (SSAM). SSAM measures the 
relative amplitude of the seismic signal in specific 
frequency bands, permitting seismologists to deter-

230 NATURAL HAZARDS: OTHER NATURAL HAZARDS
mine which frequencies dominate a signal. Different 
seismic events generate signals with different characteristics. 
The system aids recognition of patterns of 
subtle seismic change prior to eruptive episodes. 
 Slow-Scan Video Camera. Approximately 50 
mi (80 km) east of Redoubt Volcano on the Kenai 
Peninsula, a slow-scan video camera was installed to 
provide images of the volcano during clear weather. 
It is nearly 3,500 times more sensitive to light than 
most home-video cameras, and thus can record at 
night. An image is transmitted every 35 seconds and 
displayed on a black-and-white monitor. The video 
system helps seismologists correlate seismic events 
with volcanic activity. 
 Lightning-Detection System. This system 
was deployed experimentally, because the cause of 
eruption lightning is uncertain. It may result from 
friction between ash (tephra) particles and steam and 
other gases within an ash plume. Eruption lightning 
discharges include both cloud-to-ground and cloud-
to-cloud strikes. During a large seismic event when 
the volcano is not visible, the presence of lightning 
dispels uncertainty in interpreting the seismicity. An 
ash plume is almost certainly present when sustained 
seismic signals and lightning occur together. For 
some episodes at Redoubt, lightning detection 
allowed scientists to conclude within minutes that an 
ash plume was forming above the volcano even 
though a plume could not be seen. 
 Debris-Flow Detection System. This installation 
consists of three stations located adjacent to 
Drift River at increasing distances from the volcano. 
Each station consists of a seismometer sensitive to 
high-frequency (10-300 Hz) ground vibrations 
caused by flowing mixtures of water and rock debris 
and a radio to send the data to a receiving station. 
The signals are separated into frequency ranges and 
continuously analyzed by computer. Flow events can 
be detected on the basis of high-frequency character, 
even during volcanic activity and earthquakes. When 
the system is operating, all debris flows triggered by 
volcanic activity are detected. 
MITIGATION APPROACHES 
Losses from volcanic eruption can be reduced in several 
ways, described below. 
 Past eruptive activity can be used to define the potential 
type, scale, location, extent, effect, and severity of 
future eruptions and to define hazard zones which can 
guide development through land-use planning. 
 Establishment of detection and monitoring systems to 
measure physical changes that precede activity can 
enhance forecasting of impending eruptions and pro-
vide warning. 
 Disaster preparedness and emergency evacuation can 
provide substantial loss reduction when the locations 
and types of hazards for a particular volcanic eruption 
are taken into consideration. Plans should be based 
on hazard-zone maps showing the relative severity, 
extent, and effect of specific volcanic eruptions. An 
important element is the development of emergency 
communication systems to warn and inform the public 
of potentially hazardous events. 
 Protective measures can be effective in reducing losses 
from certain volcanic hazards. Relatively simple 
actions such as providing high-efficiency dust masks 
and goggles can protect people from respiratory dam-
age and eye irritation. Changing oil and air filters can 
reduce damage to vehicles due to ashfalls. However, 
effective and economically feasible diversion or control 
lava flows, pyroclastic flows, and debris flows 
generally is not possible. 
 Risk assessment, especially coupled with land-use 
planning, provides a strategy for reducing losses from 
volcanic hazards. Risk assessment involves deter-
mining the value of affected resources, the exposure 
of those resources, and the probability that a volcanic 
eruption of a certain magnitude will take place with-
in a certain period of time. On the basis of the risk 
assessment, land-use decisions can be made that are 
consistent with goals for public safety. 
RECOMMENDATIONS 
Wright and Pierson (1992) describe several challenges 
for the future to improve the understanding of volcanic 
activity and the ability to communicate scientific results 
in a way that can be used by communities facing volcanic 
hazards: 
 Early detection of volcanic unrest and potential eruption 
through establishment of telemetering networks 
to monitor baseline seismic activity (seismometers) 
and ground deformation (Global Positioning 
Systems); 
 Volcanic hazard assessments at several active or 
potentially active U.S. volcanoes using GIS technology 
and computer models to study the paths of lava 
flows, debris flows, and debris avalanches; 

 Research in volcanic processes using sophisticated 
geophysical techniques to improve the understanding 
of magma-water interactions, large-scale debris 
avalanches, large debris flows and related sediment-
laden flood waves; and 
 Improved communications and the development of 
emergency response plans that can be put in place 
quickly in areas that show signs of volcanic unrest, 
and the development and distribution of nontechnical 
publications that describe volcanic hazards and 
lessons learned from previous eruptions 
BIBLIOGRAPHY AND REFERENCES 
Brantley, S.R. (Ed.) 1990. The Eruption of Redoubt 
Volcano, Alaska, December 14, 1989-August 31, 1990. 
U.S. Geological Survey Circular 1061. 
Brantley, S.R. 1994. Volcanoes of the United States. 
U.S. Geological Survey. 
Beverage, J.P., and J.K. Culbertson. 1964. 
"Hyperconcentrations of Suspended Sediment." 
Journal of the Hydraulics Division. American Society 
of Civil Engineers. Vol. 90, No. HY6, pp. 117-126. 
Coch, N.K. 1995. GEOHAZARDS: Natural and 
Human. Upper Saddle River, NJ: Prentice Hall. 
Crandell, D.R. 1984. Catastrophic Debris Avalanche 
from Ancestral Mount Shasta Volcano, California." 
Geology. Vol. 12, pp. 143-146. 
Hays, W.W. 1981. Facing Geologic and Hydrologic 
Hazards: Earth-Science Considerations. U.S. 
Geological Survey Professional Paper 1240-B. 
Heliker, C. 1990. Volcanic and Seismic Hazards on 
the Island of Hawaii. U.S. Geological Survey. 
Hoblitt, R.P., C.D. Miller, and W.E. Scott. 1987. 
Volcanic Hazards with Regard to Siting Nuclear-
Power Plants in the Pacific Northwest. U.S. 
Geological Survey Open-File Report 87-297. 
Lipman, P.W., and D.R. Mullineaux (eds). 1981. The 
1980 Eruptions of Mount St. Helens, Washington. 
U.S. Geological Survey Professional Paper 1250. 
Miller, C.D. 1989. Potential Hazards from Future 
Volcanic Eruptions in California. U.S. Geological 
Survey Bulletin 1847. 
Motyka, R.J., S.A. Liss, C.J. Nye, and M.A. Moorman. 
1993. Geothermal Resources of the Aleutian Arc. 
Alaska Division of Geological and Geophysical Surveys 
Professional Report 114. 
Mullineaux, D.R. 1976. Preliminary Overview Map of 
Volcanic Hazards in the 48 Conterminous United 
States. Scale 1:7,500,000. U.S. Geological Survey 
Miscellaneous Field Studies Map MF-786. 
Newhall, C.G. 1984. Semiquantitative Assessment of 
Changing Volcanic Risk at Mount St. Helens, 
Washington. U.S. Geological Survey Open-File Report 
84-272. 
Pierson, T.C. 1985. "Initiation and Flow Behavior of 
the 1980 Pine Creek and Muddy River Lahars, Mount 
St. Helens, Washington." Geological Society of 
America Bulletin. Vol. 96, pp. 1056-1069. 
Pierson, T.C., and J.E. Costa. 1987. "A Rheologic 
Classification of Subaerial Sediment-Water Flows." 
Geological Society of America, Reviews in 
Engineering Geology. Vol. 7, pp. 1-12. 
Simkin, T. 1981. Volcanoes of the World: A Regional 
Directory, Gazatteer, and Chronology of Volcanism 
During the Last 10,000 Years. Stroudsburg, PA: 
Hutchinson Ross Publishing Co. 
Steenblik, J.W. 1990. "Volcanic Ash: A Rain of Terra." 
Airline Pilot, pp. 9-15. 
Voight, B., H.X. Glicken, R.J. Janda, and P.M. 
Douglass. 1981. "Catastrophic Rockslide Avalanche of 
May 18." In The 1980 Eruptions of Mount St. Helens, 
Lipman, P.W., and D.R. Mullineaux (eds.). U.S. 
Geological Survey Professional Paper 1250. 
Wright, T, L., and T.C. Pierson. 1992. Living with 
Volcanoes: The U.S. Geological Survey's Volcano 
Hazards Program. U.S. Geological Survey Circular 
1073. 



234 NATURAL HAZARDS
Chapter Summary
P
eriodic forest, grassland, and tundra fires are part of 
the natural environment, as natural and as vital as 
rain, snow, or wind (Mutch, 1995a). Wildfires are 
fueled by naturally occurring or non-native species of 
trees, brush, and grasses. Topography, fuel, and weather 
are the three principal factors that impact wildfire hazards 
and behavior. 
Wildfires occur in virtually all of the United States. The 
Western States, with their more arid climate and prevalent 
conifer and brush fuel types, are subject to more frequent 
wildfires. Wildfires have proven to be the most destructive 
in California, but they have become an increasingly frequent 
and damaging phenomenon nationwide. People are 
becoming more vulnerable to wildfires by choosing to live 
in wildland settings, and the value of exposed property is 
increasing at a faster rate than population. 
Most of the tools, data, and methodologies necessary to 
accurately assess wildfire risk and exposure on a national 
basis are not yet in place. However, the use of GIS technology, 
combined with the increased availability and utilization 
of satellite data, should facilitate progress. 
Mitigation and rapid emergency response are the most 
effective activities for reducing the short-term impact of 
wildfires. However, the emphasis of Federal land management 
agencies is shifting from suppression toward mitigation 
and overall fire management, including the use of 
prescribed fires to reduce future risks. 
Successful wildfire mitigation strategies can be complex, 
involving the participation of property owners who choose 
to live in at-risk areas, as well as many agencies, organizations, 
and individuals. 

Photo: Red Cross 

236 NATURAL HAZARDS
HAZARD IDENTIFICATION 
The four categories of wildfires that are experienced 
throughout the United States are described below. 
 Wildland fires are fueled almost exclusively by natural 
vegetation. They typically occur in national 
forests and parks, where Federal agencies are responsible 
for fire management and suppression. 
 Interface or intermix fires are urban/wildland fires 
in which vegetation and the built-environment pro-
vide fuel. 
 Firestorms are events of such extreme intensity that 
effective suppression is virtually impossible. 
Firestorms occur during extreme weather and generally 
burn until conditions change or the available fuel 
is exhausted. 
 Prescribed fires and prescribed natural fires are 
fires that are intentionally set or selected natural fires 
that are allowed to burn for beneficial purposes. 
U.S. Forest Service (USFS) figures for 1990 indicate 
that 25.7 percent of wildfires reported were caused by 
arson. Other ignition sources were debris burns (24 
percent); lightning (13.3 percent); and other (16.7 per-
cent). Lightning can present particularly difficult problems 
when dry thunderstorms move across an area that 
is suffering from seasonal drought. Multiple fires can 
be started simultaneously. In dry fuels, these fires can 
cause massive damage before containment. 
Three principal factors have a direct impact on the 
behavior of wildfires: topography, fuel, and weather. 
Other hazards may trigger wildfires, and wildfires con-
tribute to other hazards 
Topography. Topography can have a powerful influence 
on wildfire behavior. The movement of air over 
the terrain tends to direct a fire's course. Gulches and 
canyons can funnel air and act as a chimney, intensifying 
fire behavior and inducing faster rates of spread. 
Similarly, saddles on ridgetops tend to offer lower resistance 
to the passage of air and will draw fires. Solar 
heating of drier, south-facing slopes produces upslope 
thermal winds that can complicate behavior. 
Slope is an important factor. If the percentage of uphill 
slope doubles, the rate of spread of wildfire will likely 
double. On steep slopes, fuels on the uphill side of the 
fire are closer physically to the source of heat. 
Radiation preheats and dries the fuel, thus intensifying 
fire behavior. Terrain can inhibit wildfires: fire travels 
downslope much more slowly than it does upslope, and 
ridgetops often mark the end of wildfire's rapid spread. 
Fuel. Fuels are classified by weight or volume (fuel 
loading) and by type. Fuel loading, often expressed in 
tons per acre, can be used to describe the amount of 
vegetative material available. If fuel loading doubles, 
the energy released also can be expected to double. 
Each fuel type is given a burn index, which is an estimate 
of the amount of potential energy that may be 
released, the effort required to contain a fire in a given 
fuel, and the expected flame length. Different fuels 
have different burn qualities. Some fuels burn more 
easily or release more energy than others. Grass, for 
instance, releases relatively little energy, but can sustain 
very high rates of spread. 
Continuity of fuels is an important factor. Continuity is 
expressed in terms of both the horizontal and vertical 
dimensions. Horizontal continuity is what can be seen 
from an aerial photograph and represents the distribution 
of fuels over the landscape. Vertical continuity 
links fuels at the ground surface with tree crowns via 
understory or "ladder" fuels. 
Another essential factor is fuel moisture. Like humidity, 
fuel moisture is expressed as a percentage of total 
saturation and varies with antecedent weather. Low 
fuel moistures indicate the probability of severe fires. 
Given the same weather conditions, moisture in fuels of 
different diameters changes at different rates. A 1,000-
hour fuel, which has a 3- to 8-in (8- to 20-cm) diameter, 
changes more slowly than a 1- or 10-hour fuel. 
Weather. Of all the factors influencing wildfire 
behavior, weather is the most variable. Extreme weather 
leads to extreme events, and it is often a moderation 
of the weather that marks the end of a wildfire's growth 
and the beginning of successful containment. High 
temperatures and low humidity can produce very vigorous 
fire activity. The cooling and higher humidity 
brought by sunset can dramatically quiet fire behavior. 
Fronts and thunderstorms can produce winds that are 
capable of radical and sudden changes in speed and 
direction, causing similar changes in fire activity. The 
rate of spread of a fire varies directly with wind velocity. 
Winds may play a dominant role in directing the 
course of a fire. The radical and devastating effect that 
wind can have on fire behavior is a primary safety concern 
for firefighters. In July 1994, a sudden change in 
wind speed and direction on Storm King Mountain led 
to a blowup that claimed the lives of 14 firefighters. 
The most damaging firestorms are usually marked by 
high winds. 

Interaction of Other Hazards. Other hazard 
events can cause wildfires, and wildfires can intensify 
other hazards. According to a 1991 case study, winds 
gusting to 62 mph (100 km/h) downed powerlines, 
resulting in 92 separate wildland fires in Washington 
(The National Wildland/Urban Interface Fire 
Protection Initiative, 1992). Earthquakes have the 
potential to cause wildfires. 
Large firestorms can create very powerful convective 
winds as air rushes in to feed the flames. These winds 
are capable of causing extensive damage but the 
ground effects are local. To the ground-level observer, 
fire and wind are perceived as one event. The upward 
rush of air in the convection column is powerful 
enough to carry burning embers far ahead of the fire 
before falling to the ground. By this spotting process, 
a fire may enlarge or create new fires. 
By removing vegetative cover, wildfires can contribute 
to mudslides, landslides, and floods. According to the 
National Commission on Wildfire Disasters, the 1992 
Foothills Fire near Boise, ID, was so hot that not only 
was the vegetation removed, but the soils were ". . . so 
heat damaged that they resist water penetration and 
cause flash runoff and erosion, as well as some that 
slide off steep slopes like dry sugar . . . " (MacLeary, 
1993). 
RISK ASSESSMENT 
Using NWS data, the U.S. Forest Service administers 
the National Fire-Danger Rating System, used to assess 
the risk of wildfire at a given time. The system is used 
to make wide-scale estimates of real-time fire potential 
and behavior for very large acreages, but not structures. 
Fuel moisture, indicative of antecedent weather, combined 
with current and forecasted weather conditions 
are the main factors considered, but a variety of data 
are used. 
A computerized network, the Weather Information 
Management System (WIMS), is the main tool used to 
organize data and to provide fire weather information. 
Input includes data from hundreds of remote automatic 
weather stations which provide data on temperature, 
humidity, wind, and fuel moisture for 1- and 10-hour 
fuels. The fuel moisture of larger fuels is determined 
by inference. 
Input data collected by the TIROS-N series of polar 
orbiting weather satellites operated by NOAA are fed 
into WIMS (Loveland and others, 1991). The data are 
downloaded daily to the Earth Resources Observation 
System (EROS) and used to compile maps showing 
U.S. land cover characteristics. 
One instrument aboard the TIROS-N satellites is the 
advanced very high resolution radiometer, an infrared 
sensor. Data from this instrument have been used to 
create a Normalized Difference Vegetation Index, 
which is essentially a measurement of vegetative 
"greenness" from which vegetative fuel moisture con-
tents may be inferred. Figure 19-1 is an example of a 
departure from average greenness map which shows 
how green vegetation is compared to its average greenness 
for the current week. Similarmap products show 
relative green where each pixel is normalized to its own 
historical range, therefore all areas (dry or wet) can 
appear relatively green at some time during the growing 
season (USDA U.S. Forest Service, 1997). 
Data from these sources can be accessed from any 
computer networked to WIMS. The most commonly 
used output is organized into reports of local Fire 
Danger Ratings. These reports include the adjective 
class rating (low to extreme), Manning Class (an indication 
of resistance to suppression), burn index (an estimate 
of flame length in light grasses), moisture content 
reading for 1,000-hour fuels, and energy release component 
(expressed in BTU per second per square foot). 
The public is informed of the adjective class rating 
through media reporting and roadside signs. Figure 
19-2 is a sample of a Fire Danger Rating Map (USDA 
U.S. Forest Service, 1997). 
Exposure 
More and more people are being exposed to wildfires 
by choosing to live in or next to wildland settings. The 
value of exposed property is increasing more rapidly, 
especially in the Western States. With their more arid 
climate and conifer and brush fuel types, Western 
States are subject to more frequent wildfires than the 
rest of the United States. Western ecosystems have 
adapted to, and have even become dependent on, wild-
fires. Wildfires play an essential role by thinning 
forests and creating stands of different species and age 
groups. 
Most of the tools, data, and methodologies necessary 
for accurate assessments of risk and exposure as they 
relate to wildfires have not been developed. However, 
the use of GIS technology by many Federal, State, and 
local agencies, combined with the increased availability 
and utilization of satellite and other remote-sensing 
data, provide a sound base for the development of 
advanced tools. 
Spatial factors include topography, fuels, weather, and 
population distribution. Topographic data are available 
and are applicable to the degree of risk at a local level. 
Knowledge of where fuels and people co-exist is essen-

238 NATURAL HAZARDS
Figure 19-1
tial, but good fuel data generally are unavailable while 
the population density in some areas can be estimated 
only. 
Weather, a short term temporal factor, is a critical indicator 
of fire potential and severity. the changes that 
time provides to the density of vegetation is a long term 
temporal factor. 
Consequences 
Historical statistics on the economic impact of wild-
fires, including resource and property losses, are avail-
able for specific, large incidents. However, reporting is 
incomplete and national statistics are not compiled. 
Therefore, accurate estimates of the economic impact 
of wildfires cannot be made. 
Virtually all of the continental United States has experienced 
and will continue to experience wildfires. 
Wildfires are the most destructive in California, but 
they have become an increasingly frequent and damaging 
phenomenon elsewhere. It is impossible to assess 
fully the extent of wildfire damage due to incomplete 
reporting. The U.S. Forest Service (USFS), which 
compiles statistics for wildfires on Federal lands, is the 
primary Federal source of information. 
According to National Interagency Fire Center statistics 
for fires on Federal lands from 1985 to 1994, an aver-
age of nearly 73,000 fires occur each year, resulting in 
over 3,000,000 acres (1,215,000 ha) burned and more 
than $411.5 million expended in suppression costs. The 
single worst event in terms of deaths in U.S. history 
occurred in Wisconsin in 1871, killing 1,182 people 
(FEMA, 1990). 
The National Fire Protection Association (NFPA) is the 
best source of data for interface losses. The NFPA 
maintains two separate databases: the Fire Incident 
Data Organization (FIDO), which is a file of news clip-
pings of actual incidents; and a statistical database of 
outdoor fires to which a fire department responded. 
The file is incomplete because not all fires are reported. 
In addition, the data do not permit determination of the 
number and value of structures lost to wildfires. 
The available statistical data on interface fire losses 
tend to be specific to a particular event or region and, 
therefore, do not facilitate tracking of long-term national 
trends. According to Phillips (1994), 3,500 homes 
were destroyed by wildfires in California between 1920 
and 1989, and well over 4,200 homes were destroyed 
between 1990 and 1993. 
In 1988 in Alaska, wildfires destroyed 2.2 million acres 
(891,000 ha) of tundra and spruce forest, nearly twice 
the normal yearly average for the State. In California, 
over 9,800 fires burned more than 175,000 acres 
(70,875 ha), destroying 400 homes, barns, and other 
structures. The majority of the damage was the result 
of a 35,000-acre (14,175-ha) fire near Sacramento in 
September, which caused an estimated $22 million in 
damage (FEMA, 1990). 
Some particularly devastating interface events that 
occurred during the 1990s are described below. 
 During the 1,600-acre East Bay Fire in Oakland, CA, 
on October 20, 1991, 25 people were killed and 150 
were injured; and 3,354 single-family homes and 456 
apartments were damaged. The total estimated dam-
age was $1.5 billion (California Office of Emergency 
Services, 1992). 
 In October 1991, rural residents of counties near 
Spokane, WA, where the population increased by 76 
percent between 1970 and 1990, reported 92 separate 
fires that burned 114 homes and 35,000 acres (14,465 
ha). The winds that fanned the fires reached speeds 
of 62 mph (NFPA, 1992). 
 Between October 25 and November 3, 1993, 21 
major wildland fires broke out in California, fanned 
by two waves of hot, dry Santa Ana winds. The fires 
collectively burned over 189,000 acres (76,500 ha) 
and destroyed 1,171 structures. Three people died 
and hundreds were injured. Combined property dam-
age was estimated at approximately $1 billion 
(Hazard Mitigation Survey Team Report, 1993). 
 In 1994, one of the worst years since the early 1900s, 
79,107 fires burned 4,073,579 acres (1,648,577 ha), 
and cost $924 million for suppression. Only 325 
homes were lost, fewer than the 10-year average 
between 1985 and 1994 (900 homes per year). 
Tragically, 34 firefighters lost their lives. On July 6, 
1994, 14 firefighters died in one terrible incident during 
the South Canyon Fire just west of Glenwood 
Springs, CO. 
Federal agencies bear a significant portion of fire suppression 
costs and losses in interface areas. Of the nearly 
$1 billion in Federal funds spent on wildfire suppression 
in 1994, 30 to 50 percent was expended on protecting 
interface areas (Federal Wildland Fire 
Management Policy and Program Review, 1995). 
During the past 20 years, seven wildfires resulted in 
major disaster declarations, with six occurring in 
California. An additional 95 wildfires have qualified 
for Federal fire suppression grants. 

240 NATURAL HAZARDS
Figure 19-2FIGURE 19-2.Sample of a fire danger rating map, June 1997. 
Source: USDA Forest Service, www.fs.fed.us/land/wfas, 1997. 
RESEARCH, DATA COLLECTION, AND 
MONITORING ACTIVITIES 
Nationally accepted models have not been developed to 
make wildfire risk or vulnerability assessments. 
However, models and methods do exist for predicting 
wildfire behavior. A computer modeling tool, 
BEHAVE uses topographic, fuel, fuel moisture, and 
weather data. BEHAVE is used by the U.S. Forest 
Service at its Florida and Missoula, MT Fire Research 
Laboratories. While a reliable indicator of fire intensity 
and rates of spread in simple fire events, the model 
has some severe limitations. Output is limited to surface 
fire behavior and more extreme wildfire events, 
such as crown fires, cannot be modeled. Farsite, a more 
advanced modeling tool configured for GIS, is currently 
under development. 
BEHAVE's shortcomings are related primarily to the 
quality of available data and the complex relationship 
between the variables. Fuel moisture and weather data 
are probably good enough to support somewhat more 
advanced models. Topography, however, is dealt with 
in only a general way and may oversimplify much of 
the intricate interaction of air flow over terrain. An 
even more significant data quality issue lies in how fuel 
data are collected. The current approach involves 
observers matching photographs of fuel models to the 
appearance of local vegetation. This is often then 
extrapolated to apply to a wide area. Although useful 
for providing a comparative fuel rating, this simple 
approach does not support advanced fire behavior modeling. 
A project under development by the Fire Behavior 
Research Work Unit of the U.S. Forest Services 
Intermountain Research Station in Missoula, MT seeks 
to incorporate EROS data into an integrated fire danger/
behavior system. Part of this project will involve 
the development of a national fuels map (Burgan and 
Hartford, 1993). This project has significant potential 
for a coarse-filter, national wildfire risk assessment 
approach. 
MITIGATION APPROACHES 
Since the 1920s, aggressive fire suppression has effectively 
excluded fire from a significant portion of the 
forestlands in the United States. As a result, stand densities 
and fuel loadings have reached unprecedented 
levels. Therefore, when wildfires do occur, they exhibit 
more unusual behavior, are more intense and damaging, 
and thus are more difficult and costly to suppress. 

The paradox of aggressive fire suppression policies is 
that putting out most small fires creates conditions that 
are conducive for large fires. The emphasis of Federal 
land management agencies is shifting from suppression 
toward mitigation and overall fire management, including 
the use of prescribed fires. 
Wildfire mitigation in the urban/wildland interface has 
primarily been the responsibility of property owners 
who choose to build and live in this vulnerable zone. 
Local officials are responsible for emergency management, 
fire protection, and land-use, building, and zoning 
regulations. State officials are involved in wildfire 
hazard issues primarily through the State forest services 
and emergency management offices. When property 
owners, local fire protection authorities, and local, 
State, and federal agencies work cooperatively, there is 
a high probability that wildfire mitigation projects will 
be developed. 
Federal participation often begins with sharing of suppression 
and recovery costs. Federal land management 
agencies have the greatest fire suppression resources 
and often participate in suppression of interface fires. 
Agency roles and cost-sharing formula depend on specific 
agreements with State and local agencies. 
The U.S. Fire Administration (USFA), a unit within 
FEMA, provides a training course on firefighting techniques 
for interface fires through the National Fire 
Academy. USFA also serves on the Federal Wildfire 
Coordination Group. FEMA provides funding for educational 
brochures and other publications addressing 
wildfire issues. 
The Emergency Education Network (EENET), an out-
reach tool used by FEMA to enhance the training and 
education of fire and emergency management specialists 
nationwide, is produced at FEMA's Emergency 
Management Institute campus. EENET programs, 
which have won national videoconferencing awards, 
cover a wide array of problems, programs, and issues, 
including public awareness aspects of the 
wildland/urban interface. 
In practice, successful wildfire strategies can be quite 
involved. The most important aspect of successful suppression 
is disruption of the continuity of fuels, 
achieved by creating firelines and fire breaks. Fuel is 
removed from the course of the fire. The time necessary 
to install firelines is gained by giving up space. 
For interface fires, where homes and other structures fill 
the space, fuel reduction is best accomplished before 
the fires begin. 
In the interface, proximity to natural fuels, building 
materials, and construction features are crucial to the 
survival of homes in a wildfire. According to the 
NFPA, the principal causes of structure loss in interface 
fires are lack of defensible space and structures built 
with combustible materials and features (Baden, 1995). 
Fuel-modification measures, such as fuel breaks and 
defensible spaces, can withstand a fire's run even in 
heavy fuels and during the worst fire conditions. The 
following is testimony to the effectiveness of fuel-modification 
measures: 
"At the height of the fire's fury, it encountered a stand 
of ponderosa pine that had been thinned two years 
earlier through a careful logging operation, then 
burned in the winter to reduce ground fuels. The racing 
crown fire, totally out of control at that encounter, 
dropped immediately to the ground as the greener, 
moister tree canopy refused to ignite, and then began 
to slow in response to reduced fuels on the ground. 
Firefighters were able to move in, build fire lines, and 
halt its advance. The thinned forest was virtually 
undamaged." (McLean, 1993) 
For those involved in mitigation efforts, the resistance 
or apathy of property owners causes the greatest frustration. 
For many years, the public was told that all 
wildfires are "bad" and suppression is the cure. Public 
consciousness changes very slowly (Gardner and others, 
1987). It will probably take considerable time, a 
vigorous re-education effort, and many disasters before 
the hazards posed by wildfires are well understood. 
The adoption of regulations requiring fire-safe construction, 
such as NFPA's Standard for Protection of 
Life and Property from Wildfire (1991) and the 
International Fire Code Institute's Urban-Wildland 
Interface Code (draft, 1995), will likely gain more sup-
port. Land-use regulation issues may be more difficult 
to address. The appreciation of land values and other 
short-term economic advantages of development often 
create an active constituency strongly opposed to regulatory 
efforts which are perceived to increase the cost of 
construction. 
With understanding and cooperation, much can be done 
to prevent or mitigate wildfire hazards. However, 
according to the report of the Operation Urban Wildfire 
Task Force, ". . . in spite of all the reports and good 
work, the message is still not reaching the public, and 
effective action is not yet being taken to reduce the fire 
threat" (Peterson, 1992). 

242 NATURAL HAZARDS
Boulder County, CO. It often takes a damaging and 
frightening wildfire event to initiate an intensive mitigation 
program. On July 9, 1989, a human-caused 
wildfire blown by strong upslope winds swept out of 
Black Tiger Gulch into the foothill community of 
Sugarloaf. Within 6 hours, 44 homes and other structures 
were destroyed and many others were damaged. 
Property losses exceeded $10 million and suppression 
costs totaled another $1 million (NFPA, 1990). As a 
result, the State of Colorado and Boulder County updated 
their wildfire mitigation plans. Concerned citizens 
and firefighters approached the County Commissioners 
for help in mitigating the wildfire hazard in their communities. 
The County Commissioners responded by creating the 
Boulder County Wildfire Mitigation Group, headed by 
staff of the County Land Use Department. The group 
grew to include representatives of the USFS, Sheriff's 
Department, Parks and Open Space, City of Boulder 
Fire Department, Colorado State Forest Service, U.S. 
Bureau of Land Management, University of Colorado, 
Colorado State University, volunteer firefighters, and 
homeowners. The cooperative effort was aimed at educating 
homeowners, providing support for community 
mitigation, and communicating needs to the County 
Commissioners. 
To identify the people and structures vulnerable to wild-
fire, to quantify the hazards, and to present information 
in a useful and meaningful format, the Wildfire 
Mitigation Group used the Land Use Department's GIS 
to develop the Wildfire Hazard Information and 
Mitigation System (WHIMS). WHIMS combines 
expertise in hazard assessment, forest management, 
land use planning, wildfire behavior, and suppression 
with fire district and community involvement. 
Elements of BEHAVE are incorporated into the hazard 
rating modeling capability. 
The City of Boulder adapted WHIMS for use under the 
name FIRMIT. Data related to each home are collected 
by volunteer firefighters during onsite visits. The 
Colorado State Forest Service provides fuel data and 
other support. 
A pilot map produced by Boulder County from 
WHIMS data, indicating roof materials by lot, is shown 
in Figure 19-3. Rated from low to high flammability, 
roof materials are: metal or tile; composite or asphalt; 
treated shake; and untreated shake. 
The Boulder County Wildfire Mitigation Group provided 
the impetus and support for regulations requiring 
that homebuilders in interface areas meet reasonable 
wildfire mitigation standards. A flexible rating system 
is used, permitting a great deal of choice. All new construction 
must meet the standards through the County's 
Site Plan Review process. These standards and the rating 
system are based on the WHIMS assumptions that 
the hazard rating elements are, in order of importance, 
topography or site location, building construction and 
design, landscaping/defensible space, access, and 
water. 
In the year after the first pilot area survey, in the Pine 
Brook Hills Fire Protection District, 22 percent of the 
homeowners took mitigative actions such as changing 
roof type, limbing tree branches, moving firewood 
away from houses, and properly identifying street 
addresses. In subsequent years, additional homeowners 
have participated through such activities as a joint 
defensible space plan for 22 adjoining properties that is 
now serving as a model for others in Boulder County. 
Since the first pilot area survey, 8 of the County's 16 fire 
districts have become involved in the WHIMS project, 
scheduled for completion by 1999. To date, almost 
2,000 parcels have been impacted by WHIMS (in 
Boulder County) or FIRMIT (in the City of Boulder), 
with an estimated 6,000 more needed for completion. 
WHIMS has encouraged participation by local fire 
departments and has created a direct interface between 
firefighters and homeowners, resulting in increased 
knowledge and awareness for both. 
Other Local Initiatives. Use of GIS as a wildfire 
assessment and mitigation tool is underway in Oakland 
and Laguna Beach, CA, and Missoula, MT (Mullenix, 
1995). 
The Northern Rockies Coordinating Group is another 
example of how cooperation leads to progress. This 
multi-jurisdictional group, formed in 1984, includes 
both wildland and structural fire protection agencies. A 
long-range interface program was initiated in 1988, 
including public education, legislative action, and modifications 
of engines serving interface areas. Group 
members approached local zoning and planning commissions 
to urge fire protection consideration in 
covenants and regulations. 
In Billings, Helena, Dillon, and Kalispell, MT, Coeur 
d'Alene, ID, and other States, interagency dispatch centers 
have been formed. Response time has improved by 
eliminating jurisdictional disputes and confusion when 
fires occur in interface areas (NFPA,1991). 

Figure 19-3FIGURE 19-3.Boulder County wildfire hazard pilot map. 
Source: Land Use Department, Boulder County, CO 

244 NATURAL HAZARDS
RECOMMENDATIONS 
The development of a national wildfire hazard mitigation 
strategy will require the participation and cooperation 
of many agencies, organizations, and individuals. 
Recommendations from several sources have been considered 
and are described below. 
 Design and implement a comprehensive educational 
campaign at both the national and local levels. The 
campaign should focus on fire ecology and ecosystem 
stewardship, wildfire risk, exposure, and sound 
mitigation measures. It should target homeowners, 
firefighters, local officials, landscapers, architects, 
foresters, builders, planners, insurance companies, 
and the media. 
 Develop a practical way to use the EROS database in 
the development of a prototype GIS and remote-sensing 
wildfire risk and vulnerability assessment tool. 
 Identify the temporal factors to be used in making 
wildfire risk and vulnerability assessments. The factors 
should be suitable for use with both EROS data 
and ground-level assessments. Methods to link historical 
data with advanced technologies should be 
considered. 
 Develop a standard methodology, using an expert 
systems approach, to rate residential structures as 
fuels. 
 Devise a methodology and provide training to local 
jurisdictions for use in the development of detailed, 
on-site wildfire risk and vulnerability assessments. 
 Develop GIS-based wildfire hazard assessment tools 
for use by Federal, State, and local agencies. These 
tools should be configured to use both EROS data and 
locally collected data. 
 Support development of advanced fire behavior modeling 
tools configured to run in the spatial context of 
GIS. 
 Create a National Wildfire Mitigation Program and 
collect wildfire statistics for the past 10 to 20 years, 
estimates of current risk and exposure, and projections 
for all local jurisdictions. 
 Test tools and methodologies by conducting a thorough 
wildfire risk and vulnerability assessment for a 
pilot project area. These data could then be provided 
to appropriate State and Federal agencies, and could 
be used for fine-filter ground-truthing of EROS data. 
 Use the National Fire Information Reporting System 
for the collection, compilation, and reporting of comprehensive 
national wildfire statistics. 
BIBLIOGRAPHY AND REFERENCES 
Baden, W. 1995. National Fire Protection Association. 
National Wildland/Urban Interface Fire Protection 
Initiative. Black Tiger Fire Case Study. 
Boulder County Land Use Department. 1995. County 
of Boulder, CO. Wildfire Hazard Identification and 
Mitigation System (WHIMS) Maps. 
Burgan, R., and R. Hartford. 1993. Monitoring 
Vegetative Greenness with Satellite Data. U.S. Forest 
Service, Intermountain Research Station, Missoula, 
MT. 
California Governor's Office of Emergency Services. 
1994. East Bay Hills Fire Operations Review Group: 
A multi-Agency Review of the October 1991 Fire in 
Oakland/Berkley Hills In: Report of the National 
Commission on Wildfire Disasters. Washington, DC. 
Cortner, G., and Bridges. 1985. "Wildfire: Managing 
the Hazard in Urbanizing Areas." Journal of Soil and 
Water Conservation. 
Dodge, M. 1972. "Forest Fuel Accumulation: A 
Growing Problem." Science Magazine, Vol. 177. 
Federal Emergency Management Agency, Hazard 
Mitigation Survey Team Report. 1993. Southern 
California Firestorms. 
Federal Emergency Management Agency, Office of 
Civil Defense. 1990. Principal Threats Facing 
Communities and Local Emergency Management 
Coordinators: A Report to the United States Senate 
Committee on Appropriations. FEMA 191. 
Washington, DC: U.S. Government Printing Office. 
Federal Emergency Management Agency, Office of 
Emergency Management. 1993. Principal Threats 
Facing Communities and Local Emergency 
Management Coordinators: A Report to the United 
States Senate Committee on Appropriations. 
Washington, DC: U.S. Government Printing Office. 
Federal Emergency Management Agency, U.S. Fire 
Administration. 1992. Report to Congress, Fiscal 
Year 1991. Washington, DC. 

Federal Emergency Management Agency, U.S. Fire 
Administration, Wildfire Section. 1994. An Overview 
of Natural Hazards in the Vicinity of Boulder, CO. 
Federal Wildland Fire Management Policy and 
Program Review. 1995. Federal Register. Vol. 60, 
No. 120, pp. 32492. 
Gale, R., and H. Cortner. 1987. People and Fire at the 
Urban Wildland Interface. U.S. Forest Service. 
Gardner, P., H. Cartner, and J. Bridges. 1985. 
Managing the Hazard in Urbanizing Areas. Journal 
of Soil and Water Conservation. Vol. 40, No. 4, P. 319. 
Gardner, P., H. Cortner, and K. Widaman. 1987. "The 
Risk Perceptions and Policy Response Toward 
Wildland Fire Hazards by Urban Home-Owners." 
Landscape and Urban Planning. No. 14, pp. 163-172. 
Grant, C. 1995. "Pushed to the Limit." National Fire 
Protection Association Journal. 
International Fire Code Institute, Urban-Wildland 
Interface Code Committee. 1995 (draft). Urban-
Wildland Interface Code. Whittier, CA. 
Kay, C. E. 1994. Aboriginal Overkill and Native 
Burning: Implications for Modern Ecosystem 
Management. Salt Lake City, UT: Utah State 
University. 
Loveland, T., and others. 1991. "Development of a 
Land-Cover Characteristics Database for the 
Conterminous U.S." Photogrametric Engineering & 
Remote Sensing. Vol 57, No. 11, pp. 1453-1463. 
MacCleary, D.W. 1994. Report of the National 
Commission on Wildfire Disasters. Washington, DC. 
Magill, A. Undated. Fire Managers Must Talk With 
People. U.S. Forest Service, Wildland Recreation and 
Urban Culture. 
McLean, H.E. 1994. The Boise Quickstep In: Report 
of the National Commission on Wildfire Disasters. 
Washington, DC. 
Mullenix, M. July 1995. "Preventing Wildfires." 
Firehouse. Page 74. 
Mutch, R. 1995a. "Prescribed Fire and the Double 
Standard." In Proceedings: Environmental 
Regulations and Prescribed Fire Conference. Tampa, 
FL. 
Mutch, R. 1995b. Need for More Prescribed Fire. In 
Proceedings: Environmental Regulation and 
Prescribed Fire Conference. Tampa, FL. 
National Fire Protection Association. 1991. Wildfire 
Strikes Home, 2nd Edition, pp. 5960. 
National Fire Protection Association. 1992. Report of 
the National Commission on Wildfire Disasters, p.8. 
National Fire Protection Association, Technical 
Committee on Forest and Rural Fire Protection. 1991. 
Standard for Protection of Life and Property. NFPA 
299. 
National Wildland/Urban Interface Fire Protection 
Initiative. 1992. Fire Storm 91 Case Study. 
Peterson, G. 1992. Report of the Operation Urban 
Wildfire Task Force. Federal Emergency Management 
Agency, Operation Urban Wildfire, p. 12. 
Phillips. 1994. Personal Communication, excerpt from 
"Report of the National Commission on Wildfire 
Disasters," p. 9. 
Pyne, S.J. 1982. Fire in America, A Cultural History 
of Wildland and Rural Fire. Princeton, NJ: Princeton 
University Press. 
Savage, M. 1989. Structural Dynamics of a Pine 
Forest in the American Southwest Under Chronic 
Human Disturbance. Doctoral Thesis, Department of 
Geography. Boulder, CO: University of Colorado. 
Shanks, Hammon, Jensen, Wallen, and Associates. 
1992. "The Fire Next Time." Geo Info Systems. Vol. 
3, No. 2, p. 35. 
Joffe, B. 1992. "Update from the Ashes: GIS Helps 
Oakland Organize to Rebuild." Geo Info Systems. Vol. 
3, No. 7, p. 43. 
Sutphen, S. 1994. The California Fires of 1993: 
Coping in Orange County. Working Paper 89. 
Boulder, CO: Natural Hazards Research and 
Applications Information Center, Institute of 
Behavioral Science, University of Colorado. 
U.S. Department of Agriculture, U.S. Forest Service. 
1997. Wildland Fire Assessment System. [Online] 
Accessible at http://www.fs.fed.us./land/wfas. 
U.S. Department of Agriculture, U.S. Forest Service, 
Fire Aviation Management. 1993. Fire Related 
Considerations and Strategies in Support of 
Ecosystem Management. Washington, DC. 

246 NATURAL HAZARDS
Veblen, T., and D. Lorenz. 1991. The Colorado Front 
Range: A Century of Ecological Change. Salt Lake 
City, UT: University of Utah Press. 
Veblen, T. 1994. Preliminary Report On: Fire 
Ecology in the Urban/Wildland Interface of Boulder 
County. Boulder, CO: University of Colorado.