Abstract Title of scholarly paper: Monitoring urban expansion and population growth within Mt. Rainier’s hazard zones Caspar Jai Chung, Master of Arts, 2010 Scholarly paper directed by: Professor John Townshend Department of Geography

Mt. Rainier is located adjacent to a large population that includes major cities such as

Seattle. These areas are likely to be exposed to lahars (mudflows) by various factors such as

intense rainstorms, earthquakes, steam explosions and collapses, meaning that a significant

population is at risk of volcanic hazard. There is evidence that lahars could travel more than 60

miles (96 km) to southern Seattle (Hoblitt, 1998). In this respect, evidence of population growth

and urban expansion around that area can be considered cause for alarm. To raise awareness of

this risk, this study monitors urban expansion and population growth trends, and conducts a

vulnerability assessment using a GIS application. The National Land Cover Database (NLCD)

for 1992 to 2001 and Census tract data for 1990 and 2000 were used for this observation; the

dasymetric mapping method was utilized to observe population distribution trends and growth.

Monitoring urban expansion and population growth within Mt. Rainier’s hazard zones

by

Caspar Jai Chung

Scholarly paper submitted to the Faculty of the Graduate School of the

University of Maryland, College Park in partial fulfillment of the requirements for the degree of

Master of Arts 2010

Advisory Committee: Professor John Townshend Professor Martha Geores

© Copyright by

Caspar Jai Chung

2010

Acknowledgement

I would like to thank Professor John Townshend for advising my graduate research. I

would also like to thank Charles Johnson, GIS Technician at Pierce County Geographic

Information Services, for information and assistance.

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Table of Contents

Acknowledgment………………………………………………………………………………….ii

Table of Contents……………………………………………………………………………...….iii

Introduction………………………………………………………………………………………..1

Mt. Rainier: History and facts……………………………………………………………………..1

Significance of volcanic risk………………………………………………………………………2

Volcanic ash……………………………………………………………………………….3

Lava flows…………………………………………………………………………………3

Pyroclastic flows…………………………………………………..………………………3

Lahars………………………………………..…………………………………………….4

Data and method……………………….………………………………………………………….6

Results……………………………………………………………………………………………..9

Discussion………………….…………………………………………………………………….17

Conclusion………………………………………………………...……………………………..19

References……………………………………………………………….……………………….21

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1. Introduction

Casita Volcano, a dormant stratovolcano located in Nicaragua, caught the world’s

attention in 1998 when a lahar occurred due to heavy hurricane precipitation (Scott et al., 2005).

The lahars flew 6 kilometers downstream from their origin and inundated the surrounding area,

including the communities of El Porvenir and Rolando Rodriguez, between 3 and 6 meters deep,

causing 2,500 fatalities (ibid.). This incident warned that volcanic hazards such as lahars can

occur without associated eruptions, potentially causing catastrophic results.

A similar incident is possible at Mt. Rainier, the mountain with the highest peak and third

greatest volume in the Cascade Range. Mt. Rainier, located in the eastern area of Pierce County

and protected as a national park, drawing numerous tourists every year, is adjacent to a larger

population than Casita Volcano is, including the major cities of Seattle and Tacoma, making the

potential hazard caused by lahars even more disastrous. Evidence that lahars have traveled to

Puget Sound, where the southern parts of Seattle and Tacoma are located, is especially

consequential for the security of the region’s residents. Once the area is inundated by lahars,

there will be not only countless fatalities but also social disruption.

In this respect, evidence of population growth and urban expansion in this area can be

considered an alarming risk. In order to raise awareness of this risk, this study offers facts about

and history of Mt. Rainier, an explanation of the significance of its vulnerability, and the results

of GIS-based monitoring of urban expansion and population growth trends within the zone of

potential lahar inundation. Volcanic travel time and distribution of schools and zoning areas

within the hazard zone are also subjected to vulnerability analysis.

2. Mt. Rainier: History and facts

Mt. Rainier was called Taco’ma, Tacobed, or Taho’ma by the American Indians (Pringel

and Scott, 2001). Its highest elevation is 14,410 feet (4,396 meters), its lowest 1,600 feet (488

meters) (Henderson, 1977). It has been formed over the past 500,000 years through untold

eruptions (Driedger and Scott, 2008). There have been 11 eruptions in the past 10,000 years,

producing pumice layers; Figure 1 shows the timeline of those eruptions (Hoblitt, 1998). The

latest, in 1894 and 1895, was reported by observers in Seattle and Tacoma (Driedger and Scott,

1

Figure 1. Record of eruptions at Mt. Rainier in the last 10,000 years (Hoblitt, 1998)

2008). As Figure 1 shows, the temporal irregularity of the eruptions makes it difficult to predict

when the next will occur (Hoblitt, 1998). In this respect, enhancing the ability to predict

eruptions in order to minimize their potential damage seems to be a critical task for

volcanologists and geologists.

3. Significance of volcanic risk

The location of Mt. Rainier near such densely populated areas as Seattle and Tacoma

could be disastrous due to volcanic hazards, including volcanic ash, lava flows, and pyroclastic

flows. The latter can also develop into lahars when snow and ice melt around the summit

(Driedger and Scott, 2003).

2

3.1 Volcanic ash

Volcanic ash is dust or sand formed by pulverization of rock by volcanic activity

(Washington, Cascades Volcano Observatory & Washington State Library, 1999). It is hot right

after the eruption but gets cooler as it travels and falls (ibid.). It is predicted to affect the eastern

part of Mt. Rainier, away from densely populated areas; however, the ash may accumulate to a

thickness of 1/3 inch or more (Driedger and Scott, 2003), causing damage to electronics or

machinery and decreasing the safety of air and ground transportation (ibid.). Although the

influence of volcanic ash is not severe enough to threaten human life, it may cause a nuisance to

residents in the affected area (Driedger and Scott, 2008). Infants, the elderly, and patients with

respiratory ailments may also greatly suffer from the ash (Washington, Cascades Volcano

Observatory & Washington State Library, 1999).

3.2 Lava flows

Lava flows are “streams of molten rock that erupt relatively non-explosively from a

volcano, then move downslope until they stop, cool, and solidify” (Hoblitt, 1998, p. 3). The fact

that Mt. Rainier is composed of andesite lava flows proves its volcanic activity and demonstrates

the presence of lava flow hazards (ibid.). Moreover, the summit cone also proves that lava flows

have occurred within the past 5,600 years (ibid.). Although lava flows much slower than a

person’s walking speed, allowing animals and people to escape it easily, anything remaining in

its path will be destroyed by burial, impact or fire (ibid.). Lava flows become much more serious

when they encounter snow and ice, leading to rapid melting and then debris flows.

3.3 Pyroclastic flows

Pyroclastic flows are “hot avalanches of lava fragments and gas formed by the collapse of

thick lava flows and eruption columns” (Driedger and Scott, 2003, p. 1). They are known to

move at speeds exceeding 20 miles per hour, occasionally even reaching 200 miles per hour

(Hoblitt, 1998). Their temperatures are usually greater than 300˚ Celsius; coupled with high

velocities, they can easily destroy anything in their path by burial, impact, or incineration (ibid.).

3

According to evidence of pyroclastic flows found at Mt. Rainier, their deposits are not abundant;

thus, they may appear not to constitute a significant volcanic hazard (ibid.), but the fact that they

can convert to debris flows like lahars once in contact with snow and ice explains why they leave

so little trace (ibid.). The danger of pyroclastic flows, capable of causing lahars, should not be

underestimated.

3.4 Lahars

Lahars, from the Indonesian word for “mudflows,” are debris flows originating in

volcanoes (Stasiuk, Hickson, and Mulder, 2003). Although lava and pyroclastic flows generated

by a volcanic eruption may cause them, lahars are not necessarily associated with volcanic

eruptions. Unstable volcano slopes can be affected by intense rainstorms, earthquakes, steam

explosions, or collapses to generate lahars (Hoblitt, 1998), whose composition is a mixture of

water and sediment (equal to or greater than 60% by volume) that behaves like wet concrete

(ibid.). Lahar particles are known to vary from ash to the size of a house; their temperature can

be very high if the source materials are young and still hot (Stasiuk, Hickson, and Mulder, 2003).

Lahars’ traveling speed ranges from tens to hundreds of kilometers per hour, and can destroy

virtually anything in their path (Hoblitt, 1998).

Compared to other volcanic hazards at Mt. Rainier, lahars are the most dangerous

because their past pathways include densely populated areas, suggesting the possibility that they

may travel to these areas again. Figure 2 shows zones for volcanic hazards including lahars,

pyroclastic flows, and lava flows on Mt. Rainier. Unlike lava and pyroclastic flows, which do

not extend their influence over 10 miles from the summit of Mt. Rainier, lahars can travel

beyond 10 miles to reach the populous Puget Sound area (Driedger and Scott, 2008). According

to Hoblitt (1998), there have been at least 60 lahar activities of various sizes in Mt. Rainier over

the last 10,000 years, of which the “Osceola Mudflow” is known, based on the geological survey,

to be the largest ever. This activity, which occurred about 5,600 years ago, was at least 10 times

greater than any other lahar activity to occur there (ibid). The event is suspected to have been

triggered by the upward movement of magma, causing a debris avalanche that then transformed

to lahars (ibid), covering 212 square miles (550 km2) in the Puget Sound lowland, including the

Seattle suburban area (ibid.). Auburn, Enumclaw, Puyallup, Buckley, and Orting are among the

4

Figure 2. Hazard zones for lahars, lava flows, and pyroclastic flows from Mt. Rainier (Hoblitt et al., 1998; US Geological Survey Open-File Report 98-428)

communities directly or indirectly influenced by lahar activity. Another activity associated with

volcanism occurred about 1,200 years ago, filling the White River valley and traveling 60 miles

(100 km) to Auburn (ibid.). Additionally, between roughly 800 and 1,000 years ago, the

5

Nisqually River valley was filled by lahars to depths between 30 and 40 feet (10 to 40 m),

flowing to Puget Sound (ibid). This type of activity is known to have occurred over a dozen

times at Mt. Rainier in the last 6,000 years (ibid.).

There is growing concern that the possibility of lahars even without volcanic eruption is

increasing due to geological activity beneath Mt. Rainier. According to the Hazard Identification

and Vulnerability Analysis (HIVA) from Pierce County (2002), the development of geothermal

hydro alteration, which deteriorates the strength of slopes with hot, acidic water, is increasing

that possibility. In particular, the slope in the upper stream of the Puyallup River is known to be

weaker than other rivers originating from Mt. Rainier, making that region more susceptible to the

development of geothermal hydro alteration (ibid).

Additionally, Mt. Rainier’s lahars can be much larger than those of Mt. St. Helens, which

is known as the most active volcano in the Cascade Range and is notorious for its cataclysmic

eruption in 1980. After the eruption, a huge landslide, the largest in recorded history, traveled

about 14 miles, contributing to the formation of destructive lahars that destroyed structures

including 27 bridges and nearly 200 homes, killing 57 people and countless wildlife, including

about 7,000 big game animals and about 12 million salmon fingerlings in hatcheries (Brantley

and Myers, 2000). The main contributor to lahars at Mt. St. Helens was ice capped in the

glaciers at the edifice; the size of the ice at Mt. Rainier is far greater. While the former had less

than 0.2 km3 of ice capped in the glaciers at the edifice before the 1980 eruption, there are

approximately 4.4 km3 of ice, more than 40 times more, in Mt. Rainier (Pierce County, 2002).

With this magnitude of ice at the edifice, in the event of an eruption, Mt. Rainier may cause far

more lahars than did Mt. St. Helens.

Evidence of past lahars and future signs of their reoccurrence place them as the greatest

volcanic threat to communities near Mt. Rainier. It is thus critical to monitor trends of

population growth and urban expansion within the lahar hazard zone; performing vulnerability

analysis based on volcanic travel time and on the distribution of schools and zoning areas therein

will also provide a solid indicator of vulnerability to lahars in the region.

4. Data and method

6

The volcano hazard data layer of lahar inundation zones around the mountain, delineated

by scientists at the Cascades Volcano Observatory (Schilling, 2008), was used to observe land

cover change and population growth over time. Of the four types of lahar inundation zones

based on recurrence intervals, Case I was used for this study. The average reoccurrence rate of

lahars in Case I was every 500 to 1,000 years for the last 5,600 years, setting the annual

probability of occurrence between 0.1 and 0.2% (Hoblitt, 1998). Case I lahars are not

necessarily associated with volcanic eruptions, meaning other factors such as heavy rainfall,

earthquakes, or steam explosions may trigger them.

The dasymetric mapping method, first created by Jeremy Mennis and Torrin Hultgren

based on Visual Basic for Applications (VBA) programming and later developed and modified

as the ArcMap extension module by Michael Gould of the U.S. Geological Survey (USGS), was

utilized to observe a population distribution trend and estimate its magnitude and growth within

the hazard zone. This method was used to circumvent the limitations of geographic entities (i.e.,

tract or block data) produced by the U.S. Census Bureau for direct observation of a study area.

One problem with using original geographic entities is that the population data within each

parcel are evenly distributed throughout the parcel, which may ignore uninhabited portions

(Sleeter and Gould, 2007). Additionally, artificial population transition at the borderlines

between mapping units decreases the accuracy not only of visualized population distribution but

also of estimated population (ibid.). Therefore, Sleeter and Gould developed the dasymetric

mapping method, which redistributes the population census tract data based on ancillary data

such as land cover information, taking into consideration urban areas where population is

concentrated and uninhabited areas (i.e., open water or perennial ice). For instance, a greater

portion of the population data will be distributed to high-density residential areas, while

uninhabited areas will have zero value. Two inputs were needed to run the dasymetric mapping

tool: a population layer and an ancillary layer. According to Sleeter and Gould (2007),

geographical data consist of areal units (i.e., polygons) whose population value can be used as

population layers; Census tract data for 1990 and 2000 were used for this study. Using Census

block data instead of Census tract data was considered, for higher accuracy of observation, but

Census block data over the hazard zone exceeded 1,000, the maximum number of record

recommended by the developer for this mapping method. Therefore, Census tract data, which

met the recommended conditions, was used. For the ancillary layer, a land cover layer divided

7

into four classes (high-density residential, low-density residential, non-urban inhabited, and

uninhabited) was used (ibid.). The National Land Cover Database (NLCD) for 1992 to 2001 was

used as an ancillary layer and divided into four classes. NLCD products are based on 30m pixels

from Landsat Thematic Mapper™. Because NLCD 1992 was downloaded as a .tif file, which is

a binary file not recognized by ArcMap, it was converted to an 8bit flat binary file using Arc,

Grid program, and ENVI. Figure 3 indicates a procedure for creating a map for population

distribution and land cover in the Mt. Rainier hazard zone.

Figure 3. Flow diagram of creating a map for population distribution and land cover

For the vulnerability assessment, shapefiles of volcanic travel time and schools were

acquired from Pierce County Geographic Information Services. Table 1 shows lahars’ travel

time zones. According to the abstract in the metadata of the volcanic travel time shapefile, the

data are based on the scenario of a lahar of volume between 10,000,000 and 100,000,000 m3

(Pierce County Planning & Land Services, 2006). The expected time for a lahar to travel from

the origin of the event, or from the time the warning alarm system is activated, is estimated and

NLCD2001

Hazard Zone Layer

Masking

Masked NLCD2001

Reclassify

Reclassified NLCD2001

CensusTract 2000 Dasymetric Method

Population in Hazard Zone

8

classified into four travel zones based on a time scale. One thing to remember is that the

scenario is not based on Case I magnitude, which is estimated to have a lahar of roughly

200,000,000 m3 in volume, meaning actual travel time could be faster than shown in this data

(ibid.).

Table 1. Volcanic time of travel

Nisqually and White River systems

Puyallup and Carbon River systems

Time Zone A Area within an estimated one-hour travel distance from the source of the event

Area within an estimated half-hour travel distance from the point where the AFM alarm is sounded

Time Zone B Area within an estimated 1.5-hour travel distance from the source of the event

Area within an estimated one-hour travel distance from the point where the AFM alarm is sounded

Time Zone C Area within an estimated two-hour travel distance from the source of the event

Area within an estimated 1.5-hour travel distance from the point where the AFM alarm is sounded

Time Zone D Area more than an estimated two-hour travel distance from the source of the event

Area more than an estimated 1.5-hour travel distance from the point where the AFM alarm is sounded

Source: Pierce County Planning & Land Services (PALS) Additionally, the zoning shapefile for Pierce County was obtained from Pierce County

Geographic Information Services in order to analyze whether any areas under planning for

development within the hazard zone might have potential risk. According to the metadata, the

data were generated for the purpose of identifying zoning and land use corresponding to the

Washington State Growth Management Act (Pierce County Planning Cartography Lab, 2009).

5. Results

The map estimating land cover class within the hazard zone for 1992 to 2001 is produced

and presented in Figures 4a and 4b. Comparing these two maps reveals remarkable trends of

urban expansion in the northwest part of the hazard zone (labeled “A” in Fig. 4a and 4b), near

9

the Seattle-Tacoma metropolitan region. This trend stands out when land classes in these maps

are reclassified into urban and non urban-uninhabited areas for 1992 to 2001, then overlaid

Figure 4a. Land cover in 1992 (NLCD)

A

10

Figure 4b. Land cover in 2001 (NLCD)

together to visualize urban growth in the region. Figure 5 shows the trend of urban expansion in

the region and provides visual information on where significant urban growth has occurred.

Table 2 indicates land cover change in the hazard zone for 1992 to 2001 (data is presented in km2

and percentage). Based on these results, the overall urban area has expanded from 80,926.2 km2

in 1992 to 145,355.4 km2 in 2001, an overall increase of about 180% (Table 3). This indicates

that the urban area expanded annually by 19.96%. At the same time, non-urban land covers

generally show a reduction in area; bare land, cultivated land, and vegetation reduced by 6.3%,

0.8%, and 7.8%, respectively (Table 4). It is strongly suspected that the influence of rapid urban

growth worked to decrease these land covers.

A

11

Figure 5. Urban growth map within the hazard zone (1992-2001)

Table 2. Land cover change in the hazard zone between 1992 and 2001

Main Land Use 1992 2001

km2 % km2 % Urban, Recreational Grasses 2,090.7 0.23 48,968.1 5.42 Low Intensity Residential 39,634.2 4.38 47,876.4 5.29 High Intensity Residential 178.2 0.02 27,004.5 2.99 Commercial Industrial, Trans. 39,023.1 4.32 21,506.4 2.38 Total Urban Area 80,926.2 8.95 145,355.4 16.07 Urban 80,926.2 8.95 145,355.4 16.07 Bare Land 92,399.4 10.22 35,588.7 3.94 Cultivation 68,920.2 7.62 61,564.5 6.81 Vegetation 561,391.2 62.08 491,141.7 54.31 Open Water 30,339.9 3.36 25,999.2 2.88 Perennial Ice, Snow 64,037.7 7.08 74,073.6 8.19 Wetlands 6,273.0 0.69 70,564.5 7.80 Total Area 904,287.6 100.00 904,287.6 100.00

12

Table 3. Urban change between 1992 and 2001

Year Urban area (km2)

Change Time span (years)

Arithmetic mean change Period km2 % (km2/year) (%/year)

1992 80,926.20 64,429.20 179.61 9 7,158.80 19.96 1992-

2001 2001 145,355.40

Table 4. Change in land class between 1992 and 2001

Class Change (%) Urban 7.1 Bare Land -6.3 Cultivation -0.8 Vegetation -7.8 Open Water -0.5 Perennial Ice, Snow 1.1 Wetlands 7.1

The population density map for the hazard zone from 1990 to 2000 was produced using

the dasymetric method and is presented in Figure 6. Comparing these maps, some regions show

a trend of increase in population density, indicating rapid population growth during this period.

Cities like Auburn (labeled “A” in Fig. 6), Sumner (labeled “B”), Puyallup (labeled “C”), Orting

(labeled “D”), and McKenna (labeled “E”) are the regions showing significant growth.

According to the results of dasymetric mapping, population within the hazard zone increased

from 136,918 in 1990 to 282,340 in 2000 (Table 5), an increase of 206% that corresponds to the

trend of urban expansion.

13

Figure 6. Population density for the hazard zone

Table 5. Population change

Year Population Change (%)

1990 136,918 206.21

2000 282,340

Attempts to identify proposed developments within the hazard zone are presented in

Figure 7. Though the proportion falling within the hazard zone was minimal, results indicated

that certain parcels designated as developments for a residential area fall therein. Zoning areas

classified as “Moderate Density Single Family” were found around cities such as Puyallup,

Sumner, and Carbonado (labeled “A”). Zoning areas classified as “Village Residential” were

identified within the hazard zone near Ashford (labeled “B”). The above findings suggest that

the government of Pierce County may need to reexamine its planning strategy.

A

B C

D

14 14

Figure 7. Zoning areas within the hazard zone

Three thematic layers (distribution of schools, urban growth, and zoning) were overlaid

by volcanic travel time layer to observe the degree of lahar hazard. Analysis of school

distribution in Pierce County shows more than 10% of schools (35 out of 308) within the hazard

zone, many of them located downstream of the Puyallup River (labeled “A” in Figure 8), which

falls between time zones B and D, where lahars can reach between one and two hours after the

arrays of five acoustic flow monitor (AFM) is initiated. AFM, installed by the USGS and Pierce

County Department of Emergency Management, is the system that detects lahars’ ground

variations (Driedger and Scott, 2008); it is computerized and monitors the flow of lahars,

signaling emergency management agencies automatically so that communities can prepare for

mitigation prior to the hazard (ibid.). The area labeled “B” in Figure 8 shows the schools less

than a half-hour travel time from the point where the AFM system is initiated. Though there are

variations on travel time, it is evident that schools in the areas labeled “A” and “B” cannot avoid

lahar influence. Additionally, remarkable urban expansion where the area labeled “A” in Figure

9 falls in time zone B, where lahars may reach in between one and 1.5 hours, indicates that rapid

urban expansion and growing population are increasing the risk of lahar hazard. The problem

gets serious when development is proposed in areas with no AFM warning system. As Table 1

indicates, the Nisqually and White Rivers are the only two rivers not equipped with warning

systems; study of zoning areas reveals that development of residential areas has been proposed

15

near Ashford on the Nisqually River (labeled “B” in Figure 7), which falls within an estimated

one-hour distance from the origin of lahars activity. This calls into question whether the

planning agency has prepared reliable mitigation plans for future residents of this area.

Figure 8. Schools within the hazard zone overlaid by volcanic time of travel

A

B

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Figure 9. Urban growth map within the hazard zone overlaid by volcanic time of travel

6. Discussion

Tilling (1992) pointed out that some of the regions around the world showing high

population concentrations with rapid growth are also some of the most volcanically active,

warning of the increased risks posed by volcanic hazards as populations continue to grow and

expand into these hazard areas (Small and Naumann, 2001; Tilling, 1992). This trend rarely

leads to catastrophic results, but when it does the fatalities and infrastructural damage involved

are tragic. For example, in 1845, the Nevado del Ruiz volcano in Colombia erupted and

destroyed communities including the town of Armero, killing nearly 1,400 residents (Stasiuk,

A

17

Hickson, and Mulder, 2003); even after rebuilding, Armero was once again destroyed by

eruptions in 1985, leaving 25,000 dead (Stasiuk, Hickson, and Mulder, 2003; Voight, 1989).

The above incident suggests that a similar event may occur in the region near Mt. Rainier should

a volcanic hazard such as lahars occur in the future. The Pierce County Natural Hazard

Mitigation Plan (2004) describes the scenario for a Case I lahar in this region: areas such as Fife,

Puyallup, parts of Sumner, Orting, and the post-industrial area of Tacoma will be inundated for

weeks by soft and muddy lahars, which will not only threatens residents’ lives but also inhibit

the flow of transportation and cleanup processes (Pierce County, 2004). Orting is projected to

never be uncovered, as the mud will be too deep to excavate (ibid.). Smaller lahars may follow

if rain falls from the upper valley of the rivers, which would push the mud from higher ground to

lower areas, filling up the side streams and valley and most likely leading to floods (ibid.).

After the areas are inundated by lahars, social disruption may occur due not only to

occurrence of fatalities but also to loss of assets, which may indicate that the exposed areas have

a shortage of resources for recovery efforts. Wood and Soulard (2009) used tax-parcel values

indicating land and content value as a unit for observing the size of assets prone to potential lahar

inundation communities surrounding Mt. Rainier and revealed the degree of loss of assets for

each community. They described tax parcels as useful assets for measuring each community’s

capability of recovery, since property taxes are a significant resource for communities to operate

social services (i.e., law enforcement and schools) and any cutbacks due to lahars would

negatively affect these services, potentially impeding recovery efforts from disasters in the long

term and pressuring residents to leave their communities (Wood and Soulard, 2009). Based on

this fact, Wood and Soulard assessed numbers and percentage of assets within the lahar hazard

zone for each community in terms of parcel value based on 2008 data (Figure 10). According to

Figures 10K and 10L, total tax-parcel values indicating land and content value estimated in the

hazard zone were approximately $8.8 billion, accounting for 2% of the total parcel values in the

four Washington counties (King, Lewis, Pierce, and Thurston) under potential lahar influence

(ibid.). The city in the hazard zone with the highest total parcel value ($1.6 billion) was Puyallup

(ibid.). Additionally, it turned out that all the parcel values of some communities, including Fife

and Orting, are contained in the hazard zone, indicating that recovery efforts after inundation by

lahars in those communities could be hampered greatly by loss of assets.

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Figure 10 (K and L). Numbers and percentage of assets within the lahar hazard zone for each community in

terms of parcel values (Wood and Soulard, 2009)

In this respect, the results of the analysis showing rapid urban expansion and population

growth should be taken as a serious matter, and mitigation strategies should be enhanced. In the

long term, policymakers will need to come up with ways to disperse the population into regions

farther from the hazard zone in order to compensate for population growth inside it. The areas

designated as new developments within the hazard zone should be reexamined by planners to

check whether existing development regulations are realistic.

7. Conclusion

This study monitored trends of urban expansion and population growth and conducted a

vulnerability assessment through a GIS application. The National Land Cover Database (NLCD)

for 1992 to 2001 and Census tract data for 1990 and 2000 were used to observe trends of

population distribution and its growth and land cover change. The dasymetric mapping method

was utilized to observe a population distribution trend and estimate its magnitude and growth

within the hazard zone. Remarkable trends of urban expansion were found in some parts of the

hazard zone; urban area has expanded by about 180%, from 80,926.2 km2 in 1992 to 145,355.4

km2 in 2001. Cities like Auburn, Sumner, Puyallup, Orting, and McKenna are the regions

showing significant growth in terms of population. According to dasymetric mapping,

population within the hazard zone increased from 136,918 in 1990 to 282,340 in 2000, a 206%

increase corresponding to rapid urban expansion. Certain regions designated as developments

19

for residential areas fall within the hazard zone. Lastly, three thematic layers (distribution of

schools, urban growth, and zoning) overlaid with a volcanic travel time layer indicated multiple

areas at risk of lahar hazard. Rapid growth of urban area was detected in the region where lahars

may reach in between one and 1.5 hours, indicating that rapid urban expansion and growing

population increase the risk of lahar hazard. Proposed development of residential areas in parts

of the hazard zone with no lahar detection systems calls into question whether Pierce County is

aware of this potential danger.

The results suggest that the urban expansion and population growth within the hazard

zone should be taken seriously and the mitigation strategy enhanced. Policymakers should

consider compensating for rapid population growth by seeking reliable and realistic long-term

ways of dispersing the population into regions farther from the hazard zone. Additionally, the

areas designated as new developments within the hazard zone should be reexamined by planners

to check whether existing development regulations are realistic. If development in these areas

proceeds as planned, planners will need to come up with reliable mitigation plans for future

residents. Further research is advised in the direction of reviewing the mitigation plan for

residents and finding ways to enhance it in order to minimize the potential damage of future

lahar activity.

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