A landslide, also known as a landslip, is a form of mass wasting that includes a wide range of ground movements, such as rockfalls, deep failure of slopes, and shallow debris flows. Landslides can occur in underwater, called a submarine landslide, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released. Landslides should not be confused with mud flows, a form of mass wasting involving very to extremely rapid flow of debris that has become partially or fully liquefied by the addition of significant amounts of water to the source material.
The March 2014 landslide engulfed 49 homes and other structures in an unincorporated neighborhood known as "Steelhead Haven" 4 mi (6.4 km) on the south side of the North Fork of the Stillaguamish River, east of Oso, Washington. It also dammed the river, causing extensive flooding upstream as well as blocking State Route 530, the main route to the town of Darrington (population 1,347), approximately 15 miles (24 km) east of Oso.
Ground vibrations generated by the Oso landslide were recorded at several regional stations and subsequently analyzed by the Pacific Northwest Seismic Network (PNSN). The initial collapse began at 10:37:22 a.m. local time (PDT; 17:37:22 UTC), lasting approximately 2.5 minutes. Debris loosened by initial collapse is believed to contain material previously disturbed and weakened by the 2006 slide. Following the initial event was another large slide occurring at 10:41:53 PDT.
Additional events, most likely smaller landslides breaking off the head scarp, continued for several hours. The last notable signal came at 14:10:15. Examination of records from the nearest seismic station 7 mi (11 km) to the southwest indicate small seismic events started around 8 a.m. the day of the slide 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.
In the days following the slide, Snohomish County Emergency Management Director John Pennington speculated a 1.1 magnitude earthquake on March 10 may have triggered the landslide. Data collected by the PNSN shows a magnitude 1.1 earthquake on that date in the vicinity of the Oso landslide (about 2 ±0.8 km to the northeast), at a depth of 3.9 ±1.9 km. Regardless, the United States Geological Survey (USGS) determined the slide was not caused by seismic activity.
The landslide occurred at the southeastern edge of Whitman Bench, a land terrace about 800 ft (240 m) above the valley floor and consisting of gravel and sand deposited during the most recent glaciation. When the Puget Lobe of the Cordilleran Ice Sheet moved south from British Columbia, Canada filling the Puget Lowland, various mountain valleys were dammed and lakes were formed. Sediment washed down from the higher mountains settled in the lake bottoms, forming a layer of clay.
To qualify for this Earthcache, you must go to this location and collect the neccessary information from the surrounding area and email or message them to me. All required information will be found on this location:
1.) What is the approximate area in acreage resulting from the mudflow?
2.) What is the approximate height of the tallest mudflow?
3.) What are the first two sentences of the description of this earthcache?
4.) Please post a photo of yourself in and around this location. (Not require, but would be nice) Please do not enter the mudslide area. Take the time to reflect and enjoy the scenery.
DISCLAIMER: If your answers are incorrect and request the correct answers, you have 24 hours to update them or I shall delete your log.