2021 Atami landslide
The Atami landslide was a natural disaster which hit the city of Atami on 3 July 2021. It was caused by heavy rainfall which resulted in significant damage to the community of Atami in Japan. The debris flow by the landslide resulted in life lost, infrastructure damage and had various health consequences. It was argued that the landslide could have been prevented or better managed by local authorities. The role of climate change is evident especially in a country like Japan that experiences heavy rainfall. Better management of land use as well as disaster preparedness are critical to prevent and better manage future landslides in Japan.
Background
In 2021, there were an estimated 972 landslide disasters in Japan. Prior to the Atami landslide there had been very heavy rainfall from 30 June 2021 with flash floods. The city received a total of 432.5mm of rainfall over the four days prior to 3 July 2021, exceeding the average monthly rainfall of 243mm.It has been discovered that there was illegal landfill management within the area of Aizomegawa River. A soil mound of over 50m high, that exceeded the permitted size regulations, triggered the landslide due to the excessive rain. Debris flow destroyed and damaged many houses and buildings. Despite issuing an emergency security order, evacuations were not completed swiftly.
There were indications highlighting the possibility of a landslide occurring in the preceding months due to the rainfall patterns and early warning systems. These signs could have been used to evacuate citizens early, specifically the elderly and vulnerable. An additional learning outcome from this event is that landfill sites need to be monitored and investigated to ensure compliance with local guidelines, and prompt action is required from the community and local authorities if non-compliant.
Location
Atami is a pacific coastal city, located 68 miles south west of Tokyo, Japan, in the eastern most tip of the Shizuoka Prefecture and northeast of the Izu Peninsula. It has a total population of 34,280 people and more than 50% of Atami's population is over 60 years old within the area of 61.78km2, according to the 2020 census.Japan has extreme wet seasons which last approximately 7.2 months from March to October. The typhoon season is usually between July and October. In Atami, within this period, there is a 32% chance of precipitation, each day. June has been highlighted as the most wet month with an average of 13.3 days having rainfall. However, September has the most rain on average at 260.6mm.
Precipitating factors
Landslides generally result from a combination of decrease in the shear strength and increase in shear stress of slope materials. In the case of the Atami landslide, three factors predominantly contributed to these phenomena- natural factors, human and administrative factors.Natural factors
Atami City is formed mainly by hills, and most of the houses and the cottages rest on steep slopes. Three days leading up to the landslide, the region experienced a maximum periodic rainfall of 449 mm with a maximum 24-hour rainfall of 260 mm. This prolonged and intense level of rainfall was unseen in previous years. Heavy rainfall combined with the geographic characteristics may have affected slope stability and played an important role in triggering the landslide.Human factors
The soil along the Atami debris flow path is composed predominantly of lava and pyroclastic fall deposits from the Hakone Volcano, which may have theoretically made this region susceptible to landslides. However, there was also a landfill formed at the head of the Aizomegawa River using illegal and inappropriate construction methods, resulting in inadequate drainage and large amount of sediments, decreasing slope stability.The Geospatial Information Authority of Japan reported that in the 10 years leading up to the Atami landslide, the area underwent a backfill process with a volume of 56,000 m3, which is equal to the volume of the Atami landslide. In addition, the Atami landslide debris was not composed predominantly of pyroclastic materials, but rather of refilled waste, implying that the Atami landslide was not caused by the inherent soil property of the region, but by the backfill of landfill waste products.
These facts suggest that human factors are also responsible for the Atami landslide.
Administrative factors
In addition to natural factors and human factors, there is evidence that inadequate administrative oversight is also partly responsible for the Atami landslide.The total volume of the landfill at the head of the Aizomegawa River reached twice the volume than that initially authorized well before the Atami landslide. Also, local regulations require that special measures be taken when the height of the landfill exceeds 15 meters, but no special measures have been taken even when the height exceeded 50 meters.
There are internal administrative documents suggesting that prefectural and city officials were aware these dangers as early as 2008, but were slow and ineffective in taking necessary steps to remove the potentially dangerous factors.
Prefectural and city officials have concluded on multiple occasions in the decade leading up to the landslide that the mound and landfill “will likely pose a risk to the lives and fortunes of residents if it collapses.” and was “at risk of washout and collapse” and that the operator “needs to correct the immediately”. Local officials have ordered business operators and landowners to rectify these conditions. However, they were not able to reinforce these orders, in part due to lack of cooperation by business operators and land owners, changes in land ownership, and difficulty contacting the responsible personnel's.
Although the local government knew of the conditions of the landfill years before the landslide, it was unable to effectively carry out the measures needed to rectify these conditions. This suggest that weak administrative oversight is also partially responsible for the Atami landslide.
Impact of Atami landslide
Landslides cause significant damage to infrastructure along with many other complications. The Atami landslide had considerable impact on the community of Atami, Japan. As a result, the 2021 Atami landslide left 27 people dead and one person was reported missing. The landslide also accounted for multiple injuries. As a result of the landslide up to 274 disaster cases were reported. Unfortunately the most vulnerable seemed to be the most affected with 60% of the affected population being elderly. Local authorities issued warnings for "life threatening conditions" and unfortunately many people were trapped in their houses.Impact on infrastructure and the community of Atami
The extent of the damage was contributed to the length of the landslide. The debris flow continued for roughly 2km and the total area affected measured up to 73 400m². The effect on the economy and infrastructure were significant with 128 houses in poor condition. Most houses are aged and in poor condition to start with which meant 50% of fatalities occurred inside buildings or houses. Up to 131 houses were completely demolished by the landslide which continued for almost 2km to the sea.The extent of damage caused by the Atami landslide was also contributed due to the high slope of almost 400m from starting point to the sea. This meant that many houses were severely damaged as the height of the debris flow surpassed double story houses. The power and velocity created by the slope as well as the long travel distance had significant destructive power.
Due to the landslide the power supply was interrupted and left most people without access to water. As a result of the floods and landslide almost 600 people were displaced and had to sought after alternative housing options. Most people had to resort to temporary housing or staying with familiar people like family and friends. Almost a year later up to 144 people still had to take up interim housing.
Preparations and local regulations were not optimal which contributed to the increased effect and impact of the landslide on Atami.
Impact and consequences on health
Short-term consequences
- Crush injuries is a common complication after landslides due to the significant load of the debris. The landslide resulted in multiple injuries and 27 deaths.- Infectious diseases is a common phenomena after landslides due to contamination of water supplies by the debris flow. Water supply was interrupted by the Atami landslide, yet no reports were released on the increase of infectious diseases.
- Water and sanitation were interrupted by the Atami landslide which increase the risk of infectious diseases. Many people of the community did not have access to clean water to drink for several days after the landslide.
Long-term consequences
- Mental health: Post-traumatic stress disorder is common after landslides. A lack of family support were prevalent due to hundreds of people displaced after the landslide, which also has an effect on mental health. Minimal reports and follow-up were done to screen the mental state of survivors of the Atami landslide.- Healthcare system: Damage to hospitals and clinics lead to a loss of resources and health care workers. Luckily, disaster management assistant teams were able to access victims and transport them to hospitals.
- The risk for vector borne diseases are increased due to long term environmental changes caused primarily by the alterations in river flow and deforestation. Long term effects on vector borne diseases are yet to be determined after the Atami landslide.