Sciency Thoughts: Hertfordshire

Saturday, 27 March 2021

Flock of Rheas on loose in southern English village.

Hertfordshire Police and Three Rivers District Council are asking people in and around the village of Maple Cross to be careful of large, flightless Birds, after a flock of Rheas (Rhea sp.) were sighted in the area. The group comprises about 20 Rheas, South American Birds similar to Ostriches, although somewhat smaller, with efforts to recapture them so far unsuccessful. The police have been unable to trace the original owners of the Birds, which appear to be completely wild, and are now looking to find a new home for them, once they have been captured. Although smaller than Ostriches, Rheas are still potentially dangerous if they feel cornered, and there have been reports of them attacking Dogs and Deer in Hertfordshire.

A Rhea on the loose in the village of Maple Cross, Hertfordshire, this week. Sian Janusz/BBC.

There are three species of Rhea, the Greater Rhea, Rhea americana, native to the grasslands of Argentina, Bolivia, Brazil, Paraguay and Uruguay, the Puna Rhea, Rhea tarapacensis, found west of the Andes in Bolivia and Chile, and the Lesser, or Darwin's Rhea, Rhea pennata, found in the Altiplano and Patagonian grasslands of Bolivia, Chile, and Argentina. The Greater and Puna Rheas are classified as Near Threatened under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species, while the Darwin's Rhea is classed as Vulnerable. All three species can legally be traded, and are sometimes kept as pets in the UK, although a flock of 20 would presumably require a large enclosure.

Flats evacuated after sinkhole opens close to residential block in St Albans, England.

All the residents of a twenty one flat residential block in St Albans, England, have been evacuated after a sinkhole opened up next to an external wall on Tuesday 6 November 2018. Emergency services were called to the building after a member of the public noticed the hole, which is about six metres across and about three metres deep, at about 5.50 GMT, and at 6.45 the decision was taken to evacuate the building. The residents have been warned to expect to be out of the property for at least two weeks.

Sinkhole adjacent to a residential building in St Albans, England, on 6 November 2018. Hertfordshire Fire and Rescue.

Sinkholes are generally caused by water eroding soft limestone or unconsolidated deposits from beneath, causing a hole that works its way upwards and eventually opening spectacularly at the surface. Where there are unconsolidated deposits at the surface they can infill from the sides, apparently swallowing objects at the surface, including people, without trace.

he approximate location of the 6 November 2018 St Albans sinkhole. Google Maps.

The precise cause of this particular sinkhole is unclear, but similar holes in the same area in the past have been linked to old old chalk mines. Chalk is a particularly soft form of limestone, and particularly prone to dissolution in water, and the old mineworkings provide both a conduit through which water can flow, and a series of voids into which groundfalls can subside should any further dissolution occur.