Source data
Oso landslide, river change and State Route 530 recovery milestones
Sources checked
- 22 March 2014Landslide crossed the valley
The slide near Oso travelled almost two kilometres. Its deposit crossed State Route 530 and blocked the North Fork Stillaguamish River. · Landslide Source 1
- 23 March 2014River overtopped the deposit
Water began flowing over a low part of the deposit within about 25 hours of the landslide. · River Source 2
- 24 March 2014Aerial surveys measured the site
The USGS assessment lists lidar at one-metre horizontal resolution and aerial imagery at 0.3-metre resolution for this date. · Survey Source 1
- 26 March 2014Crews opened an alternate access route
State and county crews cleared the Mountain Loop Highway as work also connected State Route 530 with a utility road for responders. · Road and access Source 3
- Early April 2014Pilot channel excavated
County and cooperating agencies cut a pilot channel in the eastern part of the deposit to speed drainage during the search effort. · River and response Source 1
- 25 April 2014Piloted public access contracted
Washington State Department of Transportation contracted work to guide public traffic on a separate utility access road. · Road and access Source 3
Show 7 more dates
- May 2014River channel re-established through the deposit
A USGS study reports a deeply inset channel 20 to 40 metres wide through the deposit by May. · River Source 2
- 30 May 2014Highway clearing completed
The county project account records about 127,000 tons of debris moved during the State Route 530 clearing project. · Road and access Source 3
- 31 May 2014Highway reopened to piloted traffic
State Route 530 reopened through the area to one-way piloted traffic. · Road and access Source 3
- 1 June 2014Standing pool receded at lower flows
USGS reports that by this date no standing pool remained at river flows below about 57 cubic metres per second. · River Source 1
- July 2014Water surface approached its earlier profile
USGS found the channel water surface about one metre above its pre-landslide profile. · River Source 2
- 22 September 2014Highway reconstruction substantially complete
The state recorded substantial completion of the emergency roadway reconstruction project. · Road and access Source 3
- First 18 monthsSediment moved downstream
USGS estimated 820,000 metric tonnes of sediment eroded from the deposit into the river over the first 18 months. · River Source 2
Choose a milestone to trace the first day, the river’s changing channel or the return of road access.
Oso landslide, river change and State Route 530 recovery milestones
Dates and measurements come from USGS field investigations and the state and county project record. River sediment estimates and road-clearing totals describe different material and use the units reported by each source.
| Source | ||||
|---|---|---|---|---|
| 22 March 2014 | Landslide crossed the valley | The slide near Oso travelled almost two kilometres. Its deposit crossed State Route 530 and blocked the North Fork Stillaguamish River. | Landslide | Source 1 |
| 23 March 2014 | River overtopped the deposit | Water began flowing over a low part of the deposit within about 25 hours of the landslide. | River | Source 2 |
| 24 March 2014 | Aerial surveys measured the site | The USGS assessment lists lidar at one-metre horizontal resolution and aerial imagery at 0.3-metre resolution for this date. | Survey | Source 1 |
| 26 March 2014 | Crews opened an alternate access route | State and county crews cleared the Mountain Loop Highway as work also connected State Route 530 with a utility road for responders. | Road and access | Source 3 |
| Early April 2014 | Pilot channel excavated | County and cooperating agencies cut a pilot channel in the eastern part of the deposit to speed drainage during the search effort. | River and response | Source 1 |
| 25 April 2014 | Piloted public access contracted | Washington State Department of Transportation contracted work to guide public traffic on a separate utility access road. | Road and access | Source 3 |
| May 2014 | River channel re-established through the deposit | A USGS study reports a deeply inset channel 20 to 40 metres wide through the deposit by May. | River | Source 2 |
| 30 May 2014 | Highway clearing completed | The county project account records about 127,000 tons of debris moved during the State Route 530 clearing project. | Road and access | Source 3 |
| 31 May 2014 | Highway reopened to piloted traffic | State Route 530 reopened through the area to one-way piloted traffic. | Road and access | Source 3 |
| 1 June 2014 | Standing pool receded at lower flows | USGS reports that by this date no standing pool remained at river flows below about 57 cubic metres per second. | River | Source 1 |
| July 2014 | Water surface approached its earlier profile | USGS found the channel water surface about one metre above its pre-landslide profile. | River | Source 2 |
| 22 September 2014 | Highway reconstruction substantially complete | The state recorded substantial completion of the emergency roadway reconstruction project. | Road and access | Source 3 |
| First 18 months | Sediment moved downstream | USGS estimated 820,000 metric tonnes of sediment eroded from the deposit into the river over the first 18 months. | River | Source 2 |