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On Saturday, March 22, 2014, at 10:37 a.m. local time, a major mudslide occurred 4 miles (6.4 km) east of Oso, Washington, United States, when a portion of an unstable hillside known as the "Hazel Landslide" collapsed, sending mud and debris across the North Fork of the Stillaguamish River and onto the adjacent river valley, covering an area of approximately 1 square mile (2.6 km). As of March 30, 2014, the Snohomish County Medical Examiner's office has confirmed that 24 people have died, a further 4 bodies have not been added to the count, and 22 people remain missing or unaccounted for as a result of the landslide. Excluding landslides caused by volcanic eruptions, earthquakes or dam collapses, this is the deadliest single landslide event in United States history.

Overview

Active earth movement at the Hazel Landslide dates back to at least 1937 with the latest landslide event engulfed nearly fifty properties in an unincorporated neighborhood known "Steelhead Haven" (named after a species of salmon that are found in the Stillaguamish). The slide dammed the river, causing extensive flooding upstream, and blocked State Route 530, the main route to the town of Darrington (population 1,347). The geologic feature itself is called the Hazel Landslide, however, the active slide events on the geologic feature are also called landslides, with the latest event being dubbed the "Oso mudslide" by the press.

The Hazel Landslide has a history of instability, and the area experienced up to 200 percent normal rainfall over the previous 45 days before the latest slide event. This event was described by witnesses as a "fast-moving wall of mud" containing trees and other debris cutting through homes directly beneath the hill. A firefighter stated, "When the slide hit the river, it was like a tsunami". A Washington state geologist stated the slide was one of the largest landslides he had personally seen. The mud, soil and rock debris left from the mudslide is 1,500 ft (460 m) long, 4,400 ft (1,300 m) wide and deposited debris 30 to 40 ft (9.1 to 12.2 m) deep.

Casualties and damage

More than 100 first responders from Snohomish and surrounding counties were dispatched to assist with medical aid and search-and-rescue efforts, including search and rescue helicopters from nearby Naval Air Station Whidbey Island. Late in the evening of March 22, 2014, Washington Lieutenant Governor Brad Owen declared a state of emergency in Snohomish County. Governor Jay Inslee toured the area by air the following day before joining county officials at a news conference. As of March 30, 2014, the Snohomish County Medical Examiner's office has officially announced 24 confirmed dead, 18 which have been identified; with a further 4 bodies which have not yet been added to the count, bringing the total number of dead to 28. Officials state they expect the number of confirmed dead to continue to rise. The number of people that remain missing and unaccounted for is 22. Five survivors of the slide are still at Harborview Medical Center in Seattle. Forty-nine homes and structures were destroyed.

The latest slide event blocked the North Fork of the Stillaguamish River which backed up eastward. By that evening, officials were concerned that the mud and debris dam could fail, causing downstream flooding. On March 23, 2014, the river began flowing through the debris dam. As of March 27, 2014, a flash flood watch issued by the National Weather Service was in effect through April 1. With the river flowing around the north end of the debris dam, the likelihood of a flash flood was determined to be very low. Following the slide, Highway 530 was closed indefinitely by the Washington State Department of Transportation with an alternative route around the slide opened when snow was cleared from the unpaved portion of Mountain Loop Highway south of Darrington.

Initiation and possible seismic precursors

The seismic signals (ground vibrations) generated by the Oso landslide were recorded at several regional seismic stations, and analyzed by the Pacific Northwest Seismic Network (PNSN). The main event began 10:37:22 am local time (PDT; 17:37:22 UTC) and lasted about 2.5 minutes. This is believed to the initial collapse of the material previously disturbed and weakened by the 2006 slide; this is the slide that impacted the neighborhood below. Another large slide occurred at 10:41:53 PDT; this may have been the collapse of the slope above the 2006 slide area that created the scarp now visible at the top of the slide area. Additional events, most likely smaller landslides breaking off the headscarp, continued for several hours. The last notable signal came 14:10:15.

Data collected by the Pacific Northwest Seismic Network (PNSN) shows a Magnitude 1.1 earthquake in the vicinity of the Oso landslide (about 2 ±0.8 km to the northeast), at a depth of 3.9 ±1.9 km, twelve days earlier on March 10. This is the quake which Snohomish County Emergency Management Director John Pennington speculated might have triggered this landslide.

Careful examination of the records from the nearest seismic station, about 7 mi (11 km) to the southwest, found many very small events that started around 8 am and stopped in the late afternoon. However, they were not detected at the next nearest seismic station. They are also seen in the days before and after the slide, but only during daylight hours. They are believed to be related to some kind of human activity. No other indications of possible precursors have been found.

Controversy

Controversy erupted on the third day of the slide (Monday, the 24th) when John Pennington, the Director of Snohomish Countys Department of Emergency Management stated at a news conference: "This was a completely unforseen slide. This came out of nowhere."

Coincidentally, the Seattle Times had published an article that morning that "Site has long history of slide problems". On Tuesday the paper followed up with a full page article on the various reports about previous slides at this location and the liklihood of more, along with the comments of geologists, engineers, and local residents, including a report that the area was known locally as "Slide Hill". Snohomish County Public Works Director Steve Thomsen was reported as saying: "A slide of this magnitude is very difficult to predict. There was no indication, no indication at all."

Another article the next day was about a 2010 study commisioned by the county (a follow up of a 2005 report) that warned that the hillside above Steelhead Drive was one of the most dangerous in the county. According to one of the authors of the 2010 report: "For someone to say that this plan did not warn that this was a risk is a falsity." The criticism of county officials got national attention when editorialized in the The New York Times.

Aside from the question of whether this slide should have been forseen is another question of what could have been done. A rock revetment installed in 1962 to protect the toe of the slide area from erosion was overrun by a slide two years later, and an effort in 2006 to move the river back 430 feet was made moot when another landslide move the river back 730 feet. The simplest option, of not building in an area exposed to both flooding and landsliding, is unpopular, and attempts to limit it have been viewed as big goverment trampling on property rights. According environmental engineer and applied geomorphologist Tracy Drury, after the 2006 slide "They didn't even stop pounding nails." As to any kind of buy-out program, Drury said: "I think we did the best we could under the constraints that nobody wanted to sell their property and move elsewhere."

Grandy Lake Forest Associates of Mount Vernon, Washington proposed a 15-acre clearcut at the upper edge of the Oso landslide zone in 2004. Washington state forester Aaron Everett stated in an interview with KUOW that the application was rejected and "The one that was approved in the end eliminated the part of the harvest that would have been inside the groundwater recharge area." Everett further states the resulting 7-acre clearcut operation went to the edge of the groundwater danger zone. An investigation is being conducted to determine whether Grandy Lake crossed into the restricted area which could theoretically feed groundwater into the landslide zone, affecting it from 16 to 27 years. Restrictions on timber harvesting in this area were designed to prevent forest practices from contributing to increased landslide risks..

Geological context

The landslide occurred at the southeastern edge of Whitman Bench, a terrace about 800 ft (240 m) above the valley floor, consisting of gravel and sand deposited during the last glaciation. When the Puget Lobe of the Cordilleran Ice Sheet came south from British Columbia and filled the Puget Lowland it dammed the various mountain valleys, forming lakes. Sediments washed down from the higher mountains settled in the lake bottoms to form a layer of clay. As the glacial ice pressed higher against the western end of Mount Frailey the water flowing around the edge of the ice from the north was forced around Mount Frailey, eventually pouring in through the long valley extending to the northwest now occupied by Lake Cavanaugh. Where this flow entered the glacial lake the sand and gravel it carried dropped out to form a delta, the remnant of which is now Whitman Bench. After the glacier retreated and released the lake the river carved out most of those deposits, leaving the former delta "hanging" approximately 650 ft (200 m) above the current valley floor.

The sand portion of this deposit has very little clay or "fines" to cement it together, so is very weak structurally. It is also sensitive to accumulations of water, as this increases the internal "pore" pressure, which contributes to failure. For the most part water infiltrating from the surface flows right through, except at the contact with the less permeable clay, where the water accumulates and forms a zone of weakness. Such variations in pore pressure and water flux are one of the primary factors leading to slope failure, the other primary factor being erosion of the base of the slope when the river impinges on it as it meanders across the valley. These conditions have created an extensive series of landslide complexes on both sides of the valley. Additionally, the history of multiple slides at this particular location, which lies across the inferred location of one of the strands of the Darrington—Devils Mountain Fault, and possibly the conjunction with the Larch Lake fault as well may be due to seismic fracturing and uplift of the underlying rock. Additional benches on the margin of Whitman Bench are due to deep-seated slumping of large blocks, which also creates planes of weakness for future slippage and channels for water infiltration.

History

According to a report from 1999:

The Hazel landslide has been active for over half a century. Thorsen (1996) noted a tight river bend impinging on the north bank with active landsliding visible in 1937 aerial photographs. The next 60 years involves two periods of relatively low landslide activity, and two periods of relatively high activity, the last of which extends to this day .

Known activity at this specific site includes the following:

• 1937: aerial photographs show active landsliding.
• 1951: mudflow from a side channel briefly blocked the river.
• 1952: movement of large, intact blocks, leaving headscarps 70 ft (21 m) high. Later photographs show persistent activity through the next decade.
• 1967 January: slump of a large block and accompanying mud flows push the river channel about 700 ft (210 m) south. This protects the toe from erosion, activity is minor for about two decades.
• 1988 November: erosion of the toe leads to another slide, and the river is again moved south, but not as far as in 1967.

• 2006: large slide blocks the river, new channel is cut to alleviate flooding.

Slope stability and effects of logging

Numerous parties have raised the question as to whether logging was a contributing factor to the 2014 Oso (aka Hazel) mudslide. Past logging on the Whitman Bench above the Hazel Landslide has been correlated to past slide events, and this has lead to concerns that recent logging may have been a contributing factor to the 2014 slide event. Further, logging activities have long been known to trigger landslides, and in the past decade, a series of spectacular landslides that followed timber harvest have heightened public awareness of linkages between logging and landslides in Washington state. Such events include the 2007 Stilllman Creek landslides, the 2007 Highway 6 landslide, and the 2009 Whatcom County landslides.

Scientists have published several reports and papers that assess the potential impact of logging on the stability of the Hazel landslide. Below is a synopsis of their findings, with emphasis on the peer-review article.

In their 1998 peer-review article on the Hazel Landslide, Miller and Sias describe the mechanisms through which timber harvest can affect the stability of the Hazel Landslide, as paraphrased below:

Timber harvest reduces the amount of water that trees remove from the soil by evapotranspiration (ET). When water accumulates in the soil, it adds mass to the soil and it reduces frictional resistance between soil (e.g. clay) layers, both of which increase the potential for slope failure. Forests reduce soil moisture both by withdrawing water from the soil through their roots, and intercepting rainfall with their canopies such that it never reaches the soil. In a warm, low elevation site such as the Hazel Landslide, conifers actively transpire throughout the year, including winter. So as rainstorms increase soil moisture levels, conifers reduce soil moisture levels, and the relative magnitude of these two dynamic opposing factors influences the potential for slope failure. Because most rainfall occurs in the late fall, winter and early spring, the ability of forests to remove water during this time is critical to reducing landslide risk. Average annual conifer forest ET at Hazel is between 45-75% of annual rainfall, and winter ET accounts for 50% or more of annual ET. Clearcuts (and hardwood forests) have almost no ability to remove water during the winter.

The underlying geology (and hence groundwater hydrology) of the glacial deposits on the Whitman Bench is complex, making it difficult to accurately differentiate between slide-prone areas, areas where forest removal would affect landslide hydrology (e.g. groundwater recharge areas) and areas where forest removal would have no effect on landslide hydrology. As an example, based on the complex hydrology-slope stability-groundwater recharge model that Miller and Sias constructed for the Hazel Landslide, the Department of Natural Resources (which regulates logging in Washington) delineated a area above as a “groundwater recharge” area. However, recent maps published in newspapers show that much of this recharge area failed during the 2014 event, indicating that it was part of the landslide itself rather than a recharge area to the slide. Miller and Sias noted the limitations of models in accurately delineating groundwater recharge areas and suggest that field measurements of water table elevations would be useful for testing the model.

Thus, while there is little disagreement as to the mechanisms whereby forest removal can affect deep-seated landslides such as the Hazel slide, there is less consensus as to the extent of the areas around such slides that should be protected from logging. As of March 31, 2014, a review of recent news articles suggests there is not yet consensus among experts as to whether the existing protective measures were sufficient to eliminate logging as a contributing factor to the 2014 landslide.

See also

• Debris flow
• Landslide
• Mass wasting
• Rotational slides

References

1. Berman, Mark (March 24, 2014). "Everything you need to know about the Washington landslide". Washington Post. Retrieved March 24, 2014.
2. ^ Snohomish County Medical Examiner’s Office (March 31, 2014). "Snohomish County Medical Examiner's Office Official Update". snohomishcountywa.gov.
3. ^ Associated Press (March 31, 2014). "Landslide Death Rises to 24". The Daily Beast.
4. ^ Snohomish County Sheriff’s Office (March 31, 2014). "Snohomish County Sheriff's Office official update". snohomishcountywa.gov.
5. ^ Miller, Daniel J.; Sias, Joan (May 1998), "Deciphering large landslides: linking hydrological, groundwater and slope stability models through GIS" (PDF), Hydrological Processes, 12 (6): 923–941, doi:10.1002/(SICI)1099-1085(199805)12:6<923::AID-HYP663>3.0.CO;2-3
6. "Landslide in Washington State". USGS. Retrieved March 25, 2014.
   • Cooper, Jonathan. "Number of missing from Washington slide plummets". San Francisco Chronicle. Retrieved March 30, 2014. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
   • "Washington mudslide update: Official death toll rises to 17 | CTV News". Ctvnews.ca. April 21, 2013. Retrieved March 29, 2014.
   • "Washington Mudslide Death Toll Hits 25". Time. March 28, 2014.
   • Sandi Doughton, UW seismometers record slide sequence, Seattle Times, March 25, 2014. Accessed March 25, 2014.
   • Susan W. Kieffer. "Major landslide in the state of Washington, USA: UPDATE(S)". Retrieved March 23, 2014.
   • Phuong Le And Manuel Valdes, 10 more bodies found in Washington state mudslide, AP, 25 March 2014
   • 16 dead; 108 reports of missing people, Seattle Times, March 24, 2014. Retrieved March 24, 2014}}
7. "Worst Landslides in U.S. History". Wunderground. Retrieved March 31, 2014.
8. "Mudslide witness: 'Everything was gone in 3 seconds'". Everett Herald. Retrieved March 23, 2014.
   • Mark Leberfinger (March 24, 2014). "Death Toll From Washington Landslide Climbs to Eight". AccuWeather.com. Retrieved March 24, 2014.
   • Elisha Fieldstadt and Alexander Smith (March 24, 2014). "Rescuers Search 'Quicksand' for Survivors of Washington Mudslide". NBC News. Retrieved March 24, 2014.
   • Angel Gonzalez, Coral Garnick, Jack Broom (March 23, 2014). "3 die in mudslide east of Arlington, 6 homes destroyed". The Seattle Times. Retrieved March 24, 2014.{{cite web}}: CS1 maint: multiple names: authors list (link)
9. Mark Leberfinger (March 24, 2014). "Death Toll From Washington Landslide Climbs to Eight". AccuWeather.com. Retrieved March 24, 2014.
10. Nancy Bartley and Ken Armstrong, Site has long history of slide problems, The Seattle Times, March 23, 2014.
    • Fresh landslide tailings depicted in aerial photograph dated 2006, with topology map comparisons (1901–1977) at NETROnline.com
    • Zahid Arab. "What caused the landslide?". KING5 News online. King5.com. Retrieved March 24, 2014.
    • "8 confirmed dead in mudslide; 18 still missing". The Seattle Times. Retrieved March 23, 2014.
    • "Death toll rises to 14 in Snohomish County landslide". KING 5 News and Associated Press. Retrieved March 24, 2014.
11. JANIS REID (March 26, 2014). "Whidbey Island agencies assist in Oso mudslide response". Whidbey News Times.
    • "Mudslide witness: 'Everything was gone in 3 seconds'". Everett Herald. Retrieved March 23, 2014.
    • Mark Leberfinger (March 24, 2014). "Death Toll From Washington Landslide Climbs to Eight". AccuWeather.com. Retrieved March 24, 2014.
    • Elisha Fieldstadt and Alexander Smith (March 24, 2014). "Rescuers Search 'Quicksand' for Survivors of Washington Mudslide". NBC News. Retrieved March 24, 2014.
    • Angel Gonzalez, Coral Garnick, Jack Broom (March 23, 2014). "3 die in mudslide east of Arlington, 6 homes destroyed". The Seattle Times. Retrieved March 24, 2014.{{cite web}}: CS1 maint: multiple names: authors list (link)
12. "Landslide kills three, injures others in Washington state". Reuters. Retrieved March 23, 2014.
13. Eric M. Johnson (March 28, 2014). "Mudslide death toll poised to soar despite dearth of details". reuters. Retrieved March 28, 2014.
    • Medical Examiner's Office (March 27, 2014). "Washington mudslide: 90 missing and 27 presumed dead as search continues".
    • Jonathan Kaminsky (March 27, 2014). "Hopes fade as 25th body found in Washington state mudslide". Reuters. Retrieved March 27, 2014.
    • Phuong Le and Manuel Valdes (March 26, 2014). Mudslide searchers press on with dogs, bare hands. Associated Press via Yahoo News. Retrieved March 26, 2014.
    • "Navy Commander John Regelbrugge III found dead in mudslide debris". Fox40.com. September 25, 2013. Retrieved March 26, 2014.
    • 25 dead, at least 90 others missing, presumed dead in landslide disaster, March 27, 2014. Retrieved March 27, 2014;
    • 14 dead; 108 reports of missing people, Seattle Times, March 24, 2014. Accessed March 24, 2014;
    • A closer look at aerial image of Highway 530 mudslide – Interactive.
14. "Flash Flood Watch". National Weather Service. Retrieved March 27, 2014.
15. "SR 530 Landslide". Washington State Department of Transportation. Retrieved March 26, 2014.
16. Allstadt, Kate (March 26, 2014), "Seismic signals generated by the March 22nd Oso Landslide", Seismo Blog: Updates and dispatches from the PNSN
17. ^ Allstadt 2014 (PNSN).
18. Doughton, Sandi (March 25, 2014), "Scientists say there's little chance tiny quake triggered slide", The Seattle Times; Lanela, Mike (March 25, 2014), "Washington state mudslide preceded by small earthquake", CBC News
19. Armstrong, Carter & Baker 2014
20. Bartley, Nancy; Armstrong, Ken (March 24, 2014), "Site has long history of slide problems", The Seattle Times, p. A4.
21. Armstrong, Ken; Carter, Mike; Baker, Mike (March 25, 2014), "'Unforseen' risk of slide? Warnings go back decades", The Seattle Times, pp. A1, A5.
22. See External links for a partial list.
23. Brunner, Jim; Berens, Michael J. (March 26, 2014), "2010 study ranked area among the most hazardous", The Seattle Times, pp. A1, A7.
24. Rob Flaner, quoted in Brunner & Berens 2014.
25. Egan, Timothy (March 29, 2014), "A Mudslide, Foretold", The New York Times, p. SR3.
26. Armstrong, Carter & Baker 2014.
27. Schwartz, John (March 29, 2014), "No Easy Way to Restrict Construction in Risky Areas", The New York Times, p. A12.
28. Armstrong, Carter & Baker 2014.
29. Concern Over Landslide-Logging Connection Near Oso Is Decades Old
30. "Oso: Clearcut Extended Into No-Logging Zone | Northwest Public Radio". Nwpr.org. Retrieved March 31, 2014.
31. Mike Baker and Justin Mayo (March 26, 2014). "Logging OK'd in 2004 may have exceeded approved boundary". Seattle Times.
32. Department of Natural Resources (March 27, 2014). "Forest Practices Protections for Timber Harvest in Landslide-Prone Areas" (PDF).
33. Miller, Daniel J. (October 1999), Hazel/Gold Basin Landslides: Geomorphic Review Draft Report (PDF), p. 1.
34. Tabor, R. W.; Booth, D. B.; Vance, J. A.; Ford, A. B. (2002), "Geologic Map of the Sauk River 30- by 60- minute quadrangle, Washington", U.S. Geological Survey, Miscellaneous Investigations map I-2592, 2 sheets and pamphlet, scale 1:100,000
35. Details on both the Mount Higgins (shows only the eastern part of the bench) and Darrington—Devils Mountain Fault geological maps. The areas of predominately gravel (which drops out first) and sand are shown as "Qgog_e" and "Qgos_e", respectively. "Qgl_e" and "Qgl_v" mark exposures of the underlying clay and silt. "Qls" marks landslide complexes.
    • Dragovich, Joe D.; Stanton, Benjamin W.; Griesel, Gerry A.; Polenz, Michael (2003), "Geologic Map of the Mount Higgins 7.5-minute Quadrangle, Skagit and Snohomish Counties, Washington" (PDF), Washington Division of Geology and Earth Resources, Open-File Report 2003-12, 1 sheet, scale 1:24,000 {{citation}}: |first3= missing |last3= (help);
    • Dragovich, Joe D.; Stanton, Benjamin (2007), "The Darrington—Devils Mountain Fault — A probably active reverse-oblique-slip fault zone in Skagit and Island Counties, Washington", Washington Division of Geology and Earth Resources, Open-File Report 2007-2, 1 sheet, scale 1:31,104
36. ^ Miller 1999, p. 1 harvnb error: multiple targets (3×): CITEREFMiller1999 (help).
37. Miller 1999, p. 4 harvnb error: multiple targets (3×): CITEREFMiller1999 (help).
38. Mount Higgins geological map; John Vidale, quoted in Doughton, Sandi (March 24, 2014), "River likely undercut slope, experts say", The Seattle Times, p. A5
39. Miller, Dan; Sias, Joan (1997), Environmental Factors Affecting the Hazel Landslide (PDF), Figure 1.3.
40. Miller 1999, p. 2 harvnb error: multiple targets (3×): CITEREFMiller1999 (help).
41. Miller 1999, pp. 2–3 harvnb error: multiple targets (3×): CITEREFMiller1999 (help).
42. Darryl Fears (March 29, 2014). "Before the Washington mudslide, warnings of the unthinkable". Washington Post.
43. Seattle Times. "State allowed logging on plateau above slope". Retrieved March 30, 2014. {{cite web}}: Text "Local News" ignored (help); Text "The Seattle Times" ignored (help)NPR. "Oso: Clearcut Extended Into No-Logging Zone". Retrieved March 30, 2014. {{cite web}}: Text "Northwest Public Radio" ignored (help)SLOG. "Is There a Connection Between the Mudslide and Our State's Historical Mishmash of Logging Regulations?". Retrieved March 30, 2014. {{cite web}}: Text "Slog" ignored (help)KUOW. "Concern Over Landslide-Logging Connection Near Oso Is Decades Old". Retrieved March 30, 2014. {{cite web}}: Text "KUOW News and Information" ignored (help)
44. Benda, L. (1988). "Report of the ID Team Investigation of the Hazel Landslide on the North Fork of the Stillaguamish River". Unpublished. DNR NW Region, FPA: 19–09420. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
45. Sidle, Roy C. (2006). Landslides: processes, prediction, and land use. Vol. 18. American Geophysical Union. ISBN 0875903223. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
46. Seattle Times. "Seattle Times: "Logging and landslides: What went wrong?"". Retrieved March 30, 2014.
47. Seattle Times. "Seattle Times: "Slides putting our highways in danger"". Retrieved March 30, 2014.
48. Bellingham Herald. "Bellingham Herald: "Lands commissioner tours landslide areas in Whatcom County" — Protecting the environment by providing legal services for forest cases of statewide significance". Retrieved March 30, 2014.
49. Miller, D (October 18, 1999). "Hazel/Gold Basin Landslides:Geomorphic Review Draft Report". {{cite journal}}: Cite journal requires |journal= (help) Miller, D. (1997). "Environmental Factors Affecting the Hazel Landslide-Level 2 watershed analysis, Hazel, Washington". {{cite journal}}: Cite journal requires |journal= (help) Miller, Daniel J. (1998). "Deciphering large landslides: linking hydrological, groundwater and slope stability models through GIS". Hydrological Processes. 12 (6): 923–941. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Benda, L. (1988). "Report of the ID Team Investigation of the Hazel Landslide on the North Fork of the Stillaguamish River". Unpublished. DNR NW Region, FPA: 19–09420. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
50. (Miller and Sias 1998)
51. Miller, D (October 18, 1999). "Hazel/Gold Basin Landslides:Geomorphic Review Draft Report". {{cite journal}}: Cite journal requires |journal= (help)
52. Miller, Daniel J. (1998). "Deciphering large landslides: linking hydrological, groundwater and slope stability models through GIS". Hydrological Processes. 12 (6): 923–941. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
53. SLOG. "Is There a Connection Between the Mudslide and Our State's Historical Mishmash of Logging Regulations?". Retrieved March 30, 2014. {{cite web}}: Text "Slog" ignored (help)NPR. "Oso: Clearcut Extended Into No-Logging Zone". Retrieved March 30, 2014. {{cite web}}: Text "Northwest Public Radio" ignored (help)
54. Miller, D. (1997). "Environmental Factors Affecting the Hazel Landslide-Level 2 watershed analysis, Hazel, Washington". {{cite journal}}: Cite journal requires |journal= (help)
55. "Forest Practices Rules". Retrieved March 31, 2014.
56. {{Cite webNPR. "Oso: Clearcut Extended Into No-Logging Zone". Retrieved March 30, 2014. {{cite web}}: Text "Northwest Public Radio" ignored (help) | last = CSM | title = Washington mudslide: logging eyed as contributing cause - CSMonitor.com | accessdate = 2014-03-30 | url = http://www.csmonitor.com/USA/2014/0328/Washington-mudslide-logging-eyed-as-contributing-cause }} KUOW. "Concern Over Landslide-Logging Connection Near Oso Is Decades Old". Retrieved March 30, 2014. {{cite web}}: Text "KUOW News and Information" ignored (help)

External links

• Snohomish County Official 530 Slide Updates.
• State Geologist David Norman discusses landslide.
• Michio Kaku, Physics Professor discusses landslides.
• Aerial History and LiDAR of the Stilliguamish Blocking Landslide
• Professor Cliff Mass, Cliff Mass Weather Blog: The Meteorological Background for the Stillaguamish Landslide
• Dr Dave Petley, The Landslide Blog: The Steelhead landslide in Oso, Washington State
• Dr Dave Petley, The Landslide Blog: Oso landslip: useful resources and the rising human cost
• Dr Dave Petley, The Landslide Blog: Oso landslide in Washington State: three people killed and the river is blocked
• Daniel J. Miller, Landslide hazards in the Stillaguamish basin (2004)
• Report on slide on North Fork Stillaguamish River near Hazel, Washington (1952)
• Daniel J. Miller, Hazel/Gold Basin landslides (1999)

• 2014 disasters in the United States
• 2014 in Washington (state)
• 2014 natural disasters
• History of Snohomish County, Washington
• Landslides in the United States
• Natural disasters in Washington (state)