GeoLog

flooding

Imaggeo on Mondays: A Colombian myth with geologic origins

Imaggeo on Mondays: A Colombian myth with geologic origins

This photograph shows El salto del Tequendama, a natural waterfall of Colombia, located in the Department of Cundinamarca at an altitude of 2400 metres above sea level and approximately 30 kilometres southwest of the country’s capital, Bogotá.

The Salto del Tequendama is a space of transit and connectivity between the warm lands of the Magdalena river basin and the cold lands of the Sumapaz paramo, a Neotropical alpine tundra located at 4,000 metres above sea level.

Dutch-Colombian geologist Thomas Van der Hammen concluded that approximately 60,000 years ago the entire savannah of Bogota (populated today by 9 million people) was covered by a large lake, known as the Humboldt Lake, and the associated wetland plants instead of the paramo vegetation seen today.

Over time, the climate became warmer and the bottom of the Humboldt Lake began to rise. 30,000 years ago, the lake’s waters were channelled through the Bogota River and led to the Salto del Tequendama, a real climate event that we Colombians received through the myth of Bochica, a legendary hero to the Colombian indigenous group the Muisca. Here is the summarised myth of Bochica and the Tequendama jump:

“… As the Muiscas had lost respect for the gods, they offended Chibchacum, who had previously been the most beloved of their gods. He decided to punish them by flooding the savanna, for which he gave birth to the Sopo and Tivito rivers, which joined their rivers to the Funza (former name of the Bogotá River). The flood ended with many crops and human lives, until the people clamored with fasting and sacrifices to Bochica to free them from that calamity. The sage Bochica appeared on the rainbow and with his golden scepter, hit the rocks allowing the water to form a gigantic waterfall. So Bochica created the Tequendama jump.”

The large lake was partially dried and separated into smaller wetlands, where Andean plants, deer, foxes, weasels and more than 100 bird species made their home.

The waterfall, famous for its size, surrounding vegetation and vapourous waters, has been widely studied since 1668, when the Bishop of Panamá, Lucas Fernández de Piedrahíta made the first written record of its mythical origin story.

During the 18th and 19th centuries in particular, the Salto was one of the most famous natural attractions both locally and worldwide, due to the waterfall’s 157-metre drop onto a circular rocky abyss in a wooded region of permanent haze.

In the 19th century, large estates, also known as haciendas, were built on the region’s wetlands, and the natural environment was converted into places for fishing, hunting and logging. Through drainage channels, communities dried up the land to establish livestock and agricultural systems. In the last century, as the city of Bogota grew in population and size, the wetlands were filled to build neighborhoods, streets and avenues.

Like many Bogotanos, on a family weekend trip to relieve the stress generated by the chaos of the city and in search of clean air, I took this picture. The Salto was and always has been a fundamental part of the Bogota family mythology.

By Maria Cristina Arenas Bautista, National University of Colombia, Department of Civil Engineering and Agricultural (Bogotá)

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: The Crossroads of Flood and Drought

Imaggeo on Mondays: The Crossroads of Flood and Drought

This picture was taken on the way back from collecting field measurements at the Lordsburg Playa in southwestern New Mexico, USA. The setting sun highlights the contrast between the dry, cracked soil and the standing water from antecedent rainfall.

A playa is a flat topographic depression in arid or semi-arid regions that contains a large amount of deposited sediment. When the surface of the playa is dry, this deposited sediment is exposed and at risk of being entrained into the atmosphere by wind.

With an extent of approximately 250 square kilometers, Lordsburg Playa is a dust ‘hot spot’ in the southwestern Unites States. Dust events originating from the playa are normally small, but they can contain high dust concentrations and occur frequently during the dry season in spring.

The Lordsburg Playa is of particular interest to the local population, as the interstate highway I-10 crosses over the region. Under windy conditions, dust emissions from the playa can drastically reduce visibility on the highway and cause severe traffic accidents.

In October 2016, I went on a one-week field trip to the playa, installing a temporary measurement site to study local dust emission mechanisms. At that time, parts of the playa were still flooded from summer monsoon precipitation. During the field trip, we observed a local, but strong dust event. The event started in the morning and peaked at around 9:00 am when visibility was reduced to a few meters for a short time. Fortunately, the dust was blown northward during this event and the highway was not affected. Visibility recovered shortly after, but small-scale dust phenomena such as dust plumes and dust devils occurred almost continuously during most of the day.

By Martina Klose, a post-doctoral researcher at the Barcelona Supercomputing Center (BSC) in Spain

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

September GeoRoundUp: the best of the Earth sciences from around the web

September GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major story and what you might have missed

This month has been an onslaught of  Earth and space science news; the majority focusing on natural hazards. Hurricanes, earthquakes and volcanic eruptions have been dominating headlines, but here we also highlight some other natural disasters which have attracted far fewer reports. Quickly recap on an action-packed month with our overview, complete with links:

Hurricanes

Thought the Atlantic hurricane season is far from over, 2017 has already shattered records: since 1st June 13 storms have been named, of which seven have gone onto become hurricanes and two registered as a category 5 storm on the Saffir-Simpson Hurricane Wind Scale. In September, Hurricanes Irma, Katia and Jose batter Caribbean islands, Mexico and the Southern U.S.; hot on the heels of the hugely destructive Hurricane Harvey which made landfall in Texas and Louisiana at the end of August. Images captured by NASA’s Operational Land Imager (OLI) on the Landsat 8 satellite show the scale of the damage caused by Hurricane Irma; while photos reveal the dire situation unfolding in Puerto Rico after Hurricane Maria.  OCHA, the United Nations Office for the coordinate of Human Affairs, released an infographic showing the impact the 2017 hurricane season has had on Caribbean islands (correct of 22nd September).

Earthquakes

At the same time, two powerful earthquakes shook Mexico in the space of 12 days causing chaos, building collapse and hundreds of fatalities.

Rumbling volcanoes

In the meantime, all eyes on the Indonesian island of Bali have been on Mount Agung which has already forced the evacuation of almost 100,000 people as the volcano threatens to erupt for the first time in 54 years. Unprecedented seismic activity around the volcano has been increasing, though no eruptive activity has been recorded yet.

Further south, the government of Vanuatu, a South Pacific Ocean nation, declared a state of emergency and ordered the evacuation of all 11,000 residents of Ambae island, as activity of its volcano, Manaro, increased. The New Zealand Defence Force (NZDF) sent an aircraft to fly over the volcano on Tuesday and discovered plumes of smoke, ash and volcanic rocks erupting from the crater.

Map of volcanic hazards for Ambae in Vanuatu. Credit: Vanatu Meteorology & Geo-hazard Department (vmgd).

The rainy season floods

The summer months mark the onset of the rainy season in regions of Sub-Saharan Africa which experience a savanna climate. Across the Arabian Sea, including the Indian subcontinent and Southeast Asia, also sees the onset of the monsoon.

Since June, widespread flooding brought on by heavy rainfall has left 56 dead and more than 185,000 homeless in Niger, one of the world’s poorest countries. But the crisis is not restricted to Niger, throughout the summer floods (and associated land and mudslides) in Africa are thought to have claimed 25 times more lives than Hurricane Harvey did.

Meanwhile Mumbai struggled when the heaviest rainfall since 2005 was recorded on 29th August, with most of Northern India experiencing widespread flooding. So far, the UN estimates that 1,200 people have lost their lives across Nepal, India and Bangladesh as a result of the rains. The Red Cross estimates that at least 41 million people have been affected by the flooding and causing the onset of a humanitarian crisis.

Record breaking temperatures and fires

Australia’s record-breaking spring heat (Birdsville, in Queensland’s outback, broke a weather record as temperatures hit 42.5C and Sydney recorded its hottest ever September day) combined with an unusually dry winter means the country is bracing itself for a particularly destructive bushfire season. Already fires rage, uncontrolled (at the time of writing), in New South Wales.

The western United States and Canada suffered one of its worst wildfire seasons to date. Earlier this month, NASA released a satellite image which showed much of the region covered in smoke. High-altitude aerosols from those fires were swept up by prevailing winds and carried across the east of the continent. By 7th September the particles were detected over Ireland, the U.K and northern France, including Paris.

Europe’s forest fire has been hugely devastating too. Much of the Mediterranean and the region North of the Black Sea continues to be in high danger of forest fires following a dry and hot summer. Fires are active in the Iberian Peninsula, Greece, and Germany (among others). Over 2,000 hectares were recently scorched by wildfires in the central mountainous area of Tejeda in Gran Canaria.

Links we liked

  • This month saw the end of NASA’s Cassini spacecraft and ESA’s Huygens probe’s spectacular journey to Saturn. After two decades of science, the mission ended on 15th September as the spacecraft crashed into the giant planet.
  • The last day of August marks the end of the Greenland snow melt season, so September was busy for scientists evaluating how the Greenland ice sheet fared in 2017.
  • “Few disciplines in today’s world play such a significant role in how society operates and what we can do to protect our future,” writes Erik Klemetti (Assoc. Prof. at Denison University), in his post on why college students should study geology.
  • The BBC launched The Prequel to its much anticipated Blue Planet II, a natural history progamme about the Earth’s oceans. Narrated by Sir Sir David Attenborough, the series will featured music by Hans Zimmer and Radiohead. The trailer is a true feast for the eyes. Don’t miss it!

The EGU story

Is it an earthquake, a nuclear test or a hurricane? How seismometers help us understand the world we live in.

Although traditionally used to study earthquakes, like the M 8.1 earthquake in Mexico,  seismometers have now become so sophisticated they are able to detect the slightest ground movements; whether they come from deep within the bowels of the planet or are triggered by events at the surface. But how, exactly, do earthquake scientists decipher the signals picked up by seismometers across the world? And more importantly, how do they know whether they are caused by an earthquake, nuclear test or a hurricane?

To find out we asked Neil Wilkins (a PhD student at the University of Bristol) and Stephen Hicks (a seismologist at the University of Southampton) to share some insights with our readers earlier on this month.

Imaggeo on Mondays: Sedimentary record of catastrophic floods in the Atacama desert

Imaggeo on Mondays: Sedimentary record of catastrophic floods in the Atacama desert

Despite being one of the driest regions on Earth, the Atacama desert is no stranger to catastrophic flood events. Today’s post highlights how the sands, clays and muds left behind once the flood waters recede can hold the key to understanding this natural hazard.

During the severe rains that occurred between May 12 and 13, 2017 in the Atacama Region (Northern Chile) the usually dry Copiapó River experienced a fast increase in its runoff. It caused the historic center of the city of Copiapó to flood and resulted in thousands of affected buildings including the University of Atacama.

The city of Copiapó (~160,000 inhabitants) is the administrative capital of this Chilean Region and is built on the Copiapó River alluvial plain. As a result, and despite being located in one of the driest deserts of the world, it has been flooded several times during the 19th and 20th century. Floods back in 2015 were among the worst recorded.

The effects of the most recent events are, luckily, significantly milder than those of 2015 as no casualties occurred. However, more than 2,000 houses are affected and hundreds have been completely lost.

During this last event, the water height reached 75 cm over the river margins. Nearby streets where filled with torrents of mud- and sand-laden waters, with plant debris caught up in the mix too. Once the waters receded, a thick bed of randomly assorted grains of sand  was deposited over the river banks and urbanized areas.

Frozen in the body of the bed, the sand grains developed different forms and structures. A layer of only the finest grained sediments, silts and clays, bears the hallmark of the final stages of the flooding. As water speeds decrease, the finest particles are able to drop out of the water and settle over the coarser particles. Finally, a water saturated layer of mud, only a few centimeters thick, blanketed the sands, preserving the sand structures in 3D.

The presence of these unusual and enigmatic muddy bedforms has been scarcely described in the scientific literature. A new study and detailed analysis of the structures will help better understand the sedimentary record of catastrophic flooding and the occurrence of high-energy out-of-channel deposits in the geological record.

By Manuel Abad and Tatiana Izquierdo, Universidad de Atacama (Chile)