Sciency Thoughts: Lanslips

Showing posts with label Lanslips. Show all posts

Monday, 31 January 2022

Flooding and landslides kill at least 21 people in São Paulo State, Brazil.

Twenty one people are now known to have died and several more are missing amid heavy rains that have battered the Brazilian state of São Paulo since Friday 28 January 2022. Over 500 000 people have been displaced from their homes by flooding events, and at least 11 to have been killed in a series of landslides triggered by the rains. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.

Flooding in the municipality of Franco da Rocha in São Paulo State, Brazil, on Sunday 30 January 2022. CNN.

Southern Brazil has a rainy season that lasts from Ocotober to March, with peak rains from mid-November to mid-January, however, this year's rains have been exceptionally strong. Brazil has suffered a string of flood-related disasters in recent years, most notably in 2011, when over 800 people died. The country has a rapidly growing population, with little effective urban planning, which has led to sprawling urban developments springing up with little thought to natural hazards, and in particular poorer neighbourhoods often expanding up unstable hillsides, with the result that when floods occur (which is not unusual) communities are often quickly overwhelmed. This years exceptional rains have led to more widespread flooding, which may also persist for longer, and there is a distinct danger that without determined action the death toll may exceed that of 2011. Such events are becoming increasingly common in Brazil, something which many climatologists are citing as direct evidence of global warming.

Wednesday, 30 December 2020

Residents evacuated after landslide hits village in Viken County, Norway.

Ten people have been injured, one of them seriously, and another eleven are missing after a landslide hit the village of Gjerdrum in Viken County, southern Norway, at about 4.00 am local time on Wednesday 30 December 2020. Several houses are reported to have been buried under mud and debris in the village, with others sliding into the hole created by the landslip, and about 900 people have been evacuated amid concerns about further landslips.

A landslide in the village of Gjerdrum in Viken County, southern Norway, on 30 December 2020. 30 December 2020. BBC.

The landslide is thought to have been of a type known as a 'quick clay' landslip, in which an entire bedding plain of clay loses its cohesion at once, and flows like a liquid, a type of landslide largely peculiar to areas of heavy Pleistocene glaciation, such as the northern coasts of Scandinavia, Russia, Alaska and Canada. Quick clay deposits were laid down in areas where the land was pushed down beneath sealevel by the weight of glaciers, and has subsequently been uplifted after the glaciers retreated. These clays typically contain far higher salt contents than other marine clays, which can be washed out by rainfall. Significantly, they generally contain significant levels of positively charged sodium cations, which entered the clay as the sea above froze, and help to bond the negatively charged clay particles together. However, sodium particles are particularly soluble in water, and easily washed out, with the effect that once a certain level of sodium has been lost, the entire bedding plane loses its cohesion.