Soils and Geology3

164 • Chapter 3 Kuiu Timber Sale FEIS

3.10 Soils and Geology 

The following discussions are based on pre-existing data combined 

with additional data collected in the field for the Kuiu Timber Sale 

project, and is confined to the Project Area and proposed units. 

Applicable soils direction is included in the Forest Plan, Chapter 4 and 

Appendix C. General and site-specific mitigation measures are listed 

in the road and unit cards. 

Within the Project Area 6,624 acres of carbonate bedrock have been 

identified along the northeastern boundary. Karst develops where 

carbonates exist due to the action of water on soluble rock. The 

dissolution of the rock results in the development of internal drainage 

that can produce sinking streams, closed depressions, and other 

solution landforms such as sinkholes, collapsed channels, and caves. 

The Tongass National Forest has developed management guidelines 

which strive to protect and maintain the function and biological 

significance of karst landscapes and caves found, per the requirements 

of the Federal Cave Resources Protection Act of 1988. All proposed 

alternatives have been modified so that no timber harvest, road 

construction, or quarry development would occur in these areas or 

along the drainages which flow to them. 

Scoping comments for the Project Area did not identify any specific 

soil related issues. The Forest Plan, however, has identified two 

concerns pertinent to proposed timber harvests that are applicable. The 

concerns are: 1) soil productivity loss due to roads, rock pits, and 

detrimental soil conditions created as a result of timber harvests, and 

2) erosion due to management-induced mass wasting (i.e. various 

types of landslides: avalanches, debris and earth flows, soil creep, 

slumps, etc.). 

Soil Quality Standards have been established to ensure that managed 

activities do not create significant impairment to the productivity of 

the land and directs that no more than 15 percent of an activity area be 

detrimentally disturbed through management practices (FSM 2554.03-

10). National Forest System (NFS) roads are considered a dedicated 

use of the soil resource and are not included when calculating 

detrimental soil conditions, whereas temporary roads are included. 

Design criteria for new NFS road and the BMPs are included in 

Appendix B and respond to any soils concerns. 

3.10.2.1 Soil Productivity 

Deep well-drained soils are the most productive for tree growth. 

Maintaining soil drainage while minimizing soil erosion are both key 

to soil productivity in the Project Area due to high annual precipitation 

3.10.1 

Karst 

3.10.2 

Soils 
Soils and Geology3

Kuiu Timber Sale FEIS Chapter 3 • 165 

and the overall topography of the area. Tree rooting in the area is 

generally shallow and soils are covered by thick matting created from 

accumulating and decaying organic matter. 

3.10.2.2 Soil Disturbance and Erosion 

Soil disturbance is part of a natural and ongoing process within a forest 

ecosystem. Erosion is considered one phase of soil disturbance, 

initiated by natural processes such as heavy or consistent precipitation, 

landslides, and windthrow. Soil disturbance can also be initiated by 

land management activities (e.g. road construction, timber harvest, and 

rock pit development (Swanston 1995). The level of disturbance varies 

with management practices and site characteristics. 

Mass movement ratings have been developed to assist management at 

the planning level for analyzing landslide potential. The value used to 

classify a rating or mass movement index (MMI) is explained in the 

Soils Specialist report available in the Kuiu Timber Sale planning 

record. The MMI ratings used, identified by Swanston (1995), are 

generally associated with the following slope gradients: 

• MMI – 1 (low): 5 to 35 percent 

• MMI – 2 (moderate): 36 to 51 percent 

• MMI – 3 (high): 52 to 72 percent 

• MMI – 4 (extreme): over 72 percent 

Two landslide inventories within Southeast Alaska, based on different 

scales, provide a relative understanding of the relationship between 

timber harvests and landslides. The first inventory, conducted by 

Swanston and Marion (1991) was based on landslides over 100 cubic 

yards in size that occurred between 1963 and 1983 in Southeast 

Alaska. They found that landslides were 3.4 times more likely to occur 

in harvested areas than in unharvested areas. Swanston (1991) noted, 

“as a general rule, landslides in harvested areas are significantly 

smaller, occur at lower elevations, develop on gentler gradients, and 

tend to travel shorter distances [than naturally induced landslides]”. 

The areas considered hazardous or most prone to landslides are those 

with steep slopes or areas with distinct slip-planes. During heavy 

rainfall or snowfall events these areas have a higher likelihood of 

failing, especially if previously disturbed by blasting for rock pits, road 

pioneering, side casting of excavated material, or ground-based 

logging (Swanston and Marion 1991). 

In the other landslide analysis, slides that occurred in Southeast Alaska 

between 1971 and 1991 were reviewed and noted by Landwehr (1998, 

unpub.) from aerial photos, regardless of their size. Landwehr’s study 

3.10.3 

Mass 

Movement 
3 Environment and Effects

166 • Chapter 3 Kuiu Timber Sale FEIS 

also concluded that landslides are more likely to occur on harvested 

areas than what would occur naturally (Table 3-59). 

Table 3-59 Landslide studies by Swanston and Marion (1991) and 

Landwehr (1998 unpub.) 

 Landslides 

20-Year 

Analysis Slides / 

unharvested 

acres 

Slides / 

unharvested 

acres 

Ratio between 

harvested and 

unharvested 

Slides / mile 

of road 

construction 

Swanston 

and Marion 

(1991) 

1963-1983 

1 slide/8,021 

acres 

1 slide/2,348 

acres 

3.42 higher in 

harvested N/A 

Landwehr 

(1998, 

unpub.) 

1971-1991 

1 slide/6,239 

acres 

1 slide/622 

acres 

10.03 higher in 

harvested 1 slide/19 mile 

One factor associated with ground-based logging practices and 

subsequent landslides includes root deterioration following a harvest. 

Where steep slopes exist, slope sheer strength is provided by the 

binding action of the roots in the soil. Following harvest, root systems 

begin to decay and the soil-root fabric begins to weaken. The 

weakened soil-root fabric can further reduce the slope safety factor 

when a moderate storm or an increase in water pressure is realized 

from frequent precipitation or snow melt and may result in a landslide 

(Ziemer 1981). In the case of a clearcut harvest, root reinforcement is 

delayed for ten to fifteen years until new growth (particularly root 

density or weight) restores slope sheer strength and the binding action 

of the soil-root fabric. 

At the Forest Planning level, areas with slope gradients of 72 percent 

or more are initially removed from the tentatively suitable timber base 

due to a higher risk of landslides; however, the Forest Supervisor or 

District Ranger at the project level may approve timber harvest on 

these slopes on a case-by-case basis. Their decision includes the 

consideration of an on-site analysis of slope stability (documented on a 

Soil Stability Investigation Report), an assessment of impacts of 

potentially accelerated erosion on downslope areas and downstream 

fish habitats, as well as other affected resources and economic factors. 

3.10.4.1 Past Actions 

Approximately 22 percent of the Project Area has been harvested in 

the past 30 years, mostly from valley bottoms and gentle slopes (Table 

3.10.4 

Existing 

Condition 
Soils and Geology3

Kuiu Timber Sale FEIS Chapter 3 • 167 

3-60). Of the 10,393 acres already harvested, 6,911 were harvested 

prior to 1980 and have had more than 25 years for root net 

reinforcement and vegetative regrowth. 

 Table 3-60. Acres previously harvested in the Kuiu Timber 

Sale Area by MMI Class 

MMI Class Project Area 

Acres 

Acres 

Harvested 

% Hazard Class 

Harvested 

1 – Low 19,284 5,273 27% 

2 – Moderate 20,862 4,668 22% 

3 – High 2,595 190 7% 

4 – Extreme 3,361 262 8% 

Totals 46,102 10,393 22% 

3.10.4.2 Mass Movement 

A landslide inventory specific to the Project Area was completed in 

December 2003 using aerial photos taken in 1998, and Forest Service 

land surveys completed in the 1960s and 1980s. Through the 

inventory, 57 known landslides were identified within the Project Area 

varying in size from 0.5 to 88 acres in both managed and natural nonmanaged areas. The 88-acre slide was a large rotational failure that 

occurred after a rain-on-snow event in December 1988. This slide 

today is partially revegetated and recovering. No units are proposed on 

or near this slide. 

Predicting landslides is difficult due to the number of factors that are 

involved and their interaction with one another. Frequent precipitation 

and windthrow are two natural events, that, when combined with 

excessive soil disturbance and root deterioration, can be catalysts for a 

landslide. 

The inventory of landslides in the Project Area found that per 1,000 

acres, landslides for MMI-1 and MMI-2 soils were two times higher in 

harvested areas than in unharvested areas (Table 3-61 and Chart 3-4). 

For MMI-4 soils, there were almost three times as many landslides in 

harvested areas compared to unharvested areas. This inventory 

analysis supports previously referenced research which stated more 

landslides occur in harvested areas (Swanston and Marion 1991, 

Landwehr 1998, unpub.). 
3 Environment and Effects

168 • Chapter 3 Kuiu Timber Sale FEIS 

Table 3-61. Inventory of landslides within the Project Area 

Unharvested acres Harvested acres 

MMI Rating Number of 

Landslides 

Number of 

slides/1000 

acresa

Number of 

Landslides 

Number of 

slides/1000 

acres

b

1 – Low 1 0.07 1 0.19 

2 – Moderate 23 1.42 14 2.99 

3 – High 3 1.25 0 N/A 

4 – Extreme 12 3.87 3 11.45 

a

Ratio was developed from unharvested acres within the Kuiu Timber Sale Area Table 3-60. b

Ratio was calculated from harvested acres within the Kuiu Timber Sale Area Table 3-60. 

Chart 3-4. Kuiu Timber Sale Area landslide comparison 

Kuiu Timber Sale Area Landslide Comparison

0 2 4 6 8 10 12

1

2

3

4

MMI Rating

Landslides Per 1,000 Acres

Harvested Acres

Unharvested Acres
46251

6403

46252

6425

46090

6441

6448

46092

6442

64026409

6409

46098

6415 6427

6412

6414

46420

46101

6425

641

641

0

0

6402

6411

6413

46127

6418 6402

46096

6417

6419

6401

6421

6422

6417

6435

46152

46154

6415

6444

644

64

5

16

46360

46355

6436 6429

6402

6408

6426

6407

6405

6415

6437

642

6

8

447

46360

6446

6404

6428

46094

6443

46021

46091

503

109b

209

207

211

418

402

404

405

103d

103c

101

504

112

302

303

305

308

307

205

204

208b

208a 208

210 212

111

401

417

412

410

409

403

414

416

415

500

1000

2000

1 500

2500

3000

1 500

1 000

150 0

3000

1500

500

500

500

5 00

2500

1500

1000

3 00 0

500

500

1000

1500

500

500

1500

1500

1500

15 0 0

1000

500

3000

1 5 00

2000

1500

2000

2000

1500

1 00 0

15 00

2000

1500

1500

500

100 0

500

500

500

1 500

500

500

1500

3000

1500

1500

1500

500

500

500

500

1500

2000

10 00

3000

2500

10 00

2500

500

2000

1500

2000

2000

500

1500

50 0

500

10 00

10 00

150 0

1 000

2000

1 500

500

1 500

2500

Saginaw Bay

Security Bay

Legend

MMI-4 Extreme ( >72% Slope Gradient)

MMI-3 High ( 52-71%)

Productive Old-Growth

Managed Stands

Lakes/Saltwater

Unit Pool

Non-National Forest

Project Area Boundary

Stream Value Class I & II

Existing Open Roads

500ft Contour Interval

Roads in Storage (Closed)

Decommissioned Roads

± u:/workspace/kuiu_roaded/feis/plots/feis_plots/f3_10soils.mxd 07-09-07 EP

Kuiu Timber Sale

Figure 3-10

MMI-3 and MMI-4 Soils within the Kuiu

Timber Sale Area

Keku Strait

Kadake

Bay

0 0.5 1 2 3 4

Miles
Soils and Geology3

170 • Chapter 3 Kuiu Timber Sale FEIS

Blank 
Soils and Geology3

171 • Chapter 3 Kuiu Timber Sale FEIS

3.10.5.1 Methods 

Data used for soil analysis comes from existing resources such as the 

Soil Resource Inventory (SRI), the landslide inventory, and field data 

collected through on-site surveys conducted throughout the summer of 

2004. Road acres are based on an average road width of 40 feet (from 

top of cutslope to toe of fillslope) or 4.85 acres per mile. 

Effects are estimated based on the following measures: 

• Estimated acres of detrimental soil conditions in harvest units 

based on yarding method, 

• Acres of timber harvest on slopes over 72 percent, acres of timber 

harvest by MMI Class and estimated numbers of landslides, and 

• Cumulative acres of soil removed from productivity by roads, 

detrimental soil conditions within harvest units, and estimated 

numbers of landslides. 

3.10.5.2. Area of Analysis 

The soils analysis area for the Kuiu Timber Sale is within the same 

boundary as that used to describe the boundary for the overall project 

(Kuiu Timber Sale Area Draft EIS, 1-10). The total area (46,102 acres) 

is selected as the boundary area for the soils analysis because it is 

naturally separated from surrounding areas by water along the 

northeast and northwest shorelines and by the general topography 

along the southeast, southwest and southern areas. 

3.10.5.3 Soil Productivity 

Detrimental soil conditions are often created by harvest activities such 

as road building and yarding activities. Literature pertaining to actual 

acres of soil impacted through detrimental disturbance is limited for 

soils within Southeast Alaska; however, a survey was performed by 

Landwehr and Nowacki (1999, unpub.) where detrimental soil 

conditions were monitored as a result of a clearcut timber harvest on 

northern Prince of Wales Island. They found that partial suspension 

and shovel yarding within the clearcut harvest areas resulted in five 

percent disturbance of the acres harvested, and helicopter yarding 

resulted in three percent disturbance. 

Table 3-62 shows an estimate of detrimental soil disturbance by 

alternative associated with harvest. Note the estimates given in Table 

3-62 are based on clearcut harvest. The partial harvest prescriptions 

would likely result in less soil displacement, therefore the numbers 

presented are considered to be conservative. 

3.10.5 

Environmental 

Consequences 
3 Environment and Effects

172 • Chapter 3 Kuiu Timber Sale FEIS 

Table 3-62. Acres of detrimental soil disturbance from harvest 

and temporary road construction by alternative 

Soil disturbance Alt 1 Alt 2 Alt 3 Alt 4 Alt 5 

Ground yarding

a,b 0 24 39 62 60 

Helicopter yarding

a,b 0 0 0 5 0 

Temporary road 

construction 0 7 10 19 17 

Total acres soil 

disturbance 0 31 49 86 77 

a

HA = Harvest Acres b

EDA = Estimated Disturbance Acres (5% ground yarding, 3% helicopter yarding)

The intent of the Regional Soil Quality Standards is to maintain soil 

productivity within acceptable standards. The Standards allow up to 15 

percent of the productive forestland to be in a detrimental condition. 

No harvest or road construction is planned for Alternative 1; any 

disturbance would be caused by natural events. All action alternatives 

would maintain the soil productivity within the acceptable standards. 

Alternative 4 is estimated to produce the highest number of acres of 

detrimental disturbance (86 acres), followed by Alternative 5 (77 

acres), Alternative 3 (49 acres) and Alternative 2 (31 acres). As stated 

earlier, the acres may be overestimated for all action alternatives, with 

the exception of Alternative 5 because they include partial harvest 

units. 

3.10.5.4 Mass Movement 

Based on analysis provided by Swanston (1991) landslide potential is 

projected to be higher (twice that in harvested versus unharvested 

areas) for all alternatives on MMI-1 and 2 soils, and three times as 

likely on MMI-4 soils. Table 3-63 shows the acres of proposed timber 

harvest by alternative within each MMI Class and Figure 3-10 shows 

the MMI-3 and MMI-4 soils within the Project Area. All proposed 

units with MMI-4 soils were determined stable through soil stability 

analyses. 
Soils and Geology3

Kuiu Timber Sale FEIS Chapter 3 • 173 

Table 3-63. Acresa of MMI in proposed units by alternative 

MMI Class Alt. 1 Alt. 2 Alt. 3 Alt. 4 Alt. 5 

1– Low 0 146 115 374 298 

2 – Moderate 0 329 669 999 894 

3 – High 0 2 2 0 2 

4 – Extreme 0 0 0 14 14 

Total Acres 0 477 786 1,387 1,208 

a

 Variations in acres are the result of rounding. 

If Alternative 1 is implemented, landslides in old-growth are still 

predicted to occur. 

The landslide and MMI soils information indicates that Alternative 4 

has the greatest potential for landslides of all the alternatives. This is 

due to the greater number of acres proposed for harvest (1,387 acres), 

the amount of harvest on MMI-4 soils (14 acres), and the amount of 

clearcut harvest proposed (1,024 acres). 

Alternative 5 would have the second highest potential for landslides 

due to the greatest amount of clearcut harvest (1,208 acres), 14 acres 

of MMI-4 soils, and 2 acres of MMI-3 soils. 

Alternative 3 would have the second least potential for landslides due 

to the amount of acres harvested (786 acres), no MMI-4 acres, and the 

low number of clearcut harvest planned (409 acres). 

Alternative 2 would have the least potential for landslides due to the 

fewest acres of harvest (477 acres), no MMI-4 soils, and the fewest 

acres planned for clearcut (197 acres). 

On-site evaluations resulted in deleting some acreage due to MMI-4 

soils. For the acreage remaining, changes included specific 

silvicultural prescriptions such as partial suspension of the logs, partial 

to full retention of trees within the MMI area, or a recommendation 

that helicopter yarding be used; all of which are documented on the 

appropriate Unit Cards (Appendix B). 

3.10.5.5 Roads 

Table 3-64 displays the miles of proposed road construction by 

alternative. As directed by the Forest Plan, no proposed new NFS and 

temporary roads would occur on slopes greater than 67 percent 

gradient, or on unstable soils. 
3 Environment and Effects

174 • Chapter 3 Kuiu Timber Sale FEIS 

All temporary roads would be built to minimum size and width with 

few turnouts. At the end of this sale the temporary roads would be 

decommissioned with structures removed (culverts) and waterbars 

added (refer to Issue 4 – Cumulative Effects of Logging and Road 

Construction on Watersheds and the Transportation section of this 

chapter for more information on structures and closures). There is no 

mechanism provided for future maintenance on temporary roads; 

therefore, proper closure of these roads is critical for maintaining 

hydrologic conditions adjacent to the road. 

Reconditioning of existing National Forest System (NFS) roads is also 

necessary on between 3.9 (Alternative 3) to 7.7 (Alternative 5) miles 

of road. Additional effects to soil productivity are expected to be 

minimal because the road prism is still in place. Sediment may be 

mobilized, but it is expected to be minimal and would be mitigated 

with Best Management Practices (BMPs). See Issue 4 – Cumulative 

Effects on Watersheds and the Fisheries sections in this chapter and 

the Unit Cards in Appendix B. 

Table 3-64. Miles of NFS and temporary road by alternative and MMI class. 

MMI Class Alt. 1 Alt. 2 Alt. 3 Alt. 4 Alt. 5 

1 – Low 0 0.6 0.3 1.5 1.0 

2 - Moderate 0 0.9 1.8 2.4 2.5 

3 – High 0 0 0 0 0 

4 - Extreme 0 0 0 0 0 

The cumulative effects analysis area for soils was the Project Area. 

The Catalog of Events for Kuiu Island was referenced in determining 

cumulative effects. Cumulative effects of the proposed actions on 

long-term soil productivity are directly related to the amount of soil 

disturbance that occurs through time. Because Alternative 4 impacts 

soils more than any other alternative, its effects are analyzed for 

cumulative effects. 

Using Landwehr’s estimates to determine detrimental soil conditions 

(five percent and three percent for shovel and helicopter logging, 

respectively), it is estimated that 336 acres would be disturbed by 

temporary road construction and harvest (Landwehr 1999). For 

Alternative 4, this includes 86 acres of detrimental soil conditions, 234 

acres from past activities, and 16 acres of reasonably foreseeable 

future activities cleared by the Crane and Rowan Mountain Timber 

Sales EIS. This equates to less than six percent disturbance from the 

past, present and reasonably foreseeable acreage involved (5,751 

3.10.6 

Cumulative 

Effects 
Soils and Geology3

Kuiu Timber Sale FEIS Chapter 3 • 175 

acres), which is well below the 15 percent threshold stated in the 

Forest Service Standards and Guidelines (FSM 2554.03-10). 

No other actions are planned in the foreseeable future within the 

Project Area. The Three Mile Timber Sale Area is on east Kuiu Island, 

outside of the Kuiu Timber Sale Area.