Lake Toba

Long, long ago, a giant volcano blew out a huge amount of ash and rock.

The ground sank, and water filled the hole to make the lake.

Tens of thousands of years ago, Toba erupted in what UNESCO calls one of the most powerful volcanic events in Earth's history, about a thousand times stronger than the 1980 eruption of Mount St. Helens. UNESCO dates it to about 75,000 years ago; NASA says around 70,000 years ago.

NASA explains that after the eruption the ground collapsed, leaving a caldera that filled with water to make Lake Toba. The US Geological Survey (USGS) says the caldera formed when the magma chamber emptied.

NASA's Earth Observatory calls the Toba eruption the largest in the past 2 million years: over what was probably a two-week span, thousands of cubic kilometers of debris spewed out, and pyroclastic flows buried at least 20,000 km² around the caldera. Ash lies in layers up to 6 m thick as far away as India.

UNESCO estimates the eruption was a thousand times stronger than Mount St. Helens in 1980 and says its ash and gases spread across South Asia and cooled the climate. NASA and the USGS describe the same sequence: the magma chamber emptied, the ground collapsed into a caldera, and water filled it.

Samosir Island in the lake was pushed up from underneath by hot melted rock.

A newer volcano also grew on the lake's shore.

NASA says Samosir Island is a resurgent dome: a mound of rock pushed up by pressure from magma still in the chamber beneath the volcano. The ash layer on Samosir is more than 600 meters thick.

A newer volcano, Pusukbukit, also formed on the western shore of the lake after the great eruption.

According to NASA, Samosir Island is a resurgent volcanic dome, rock uplifted by pressure from un-erupted magma in the chamber beneath the volcano, and the Toba ash on Samosir is more than 600 m thick. The Pusukbukit volcano on the western shore also formed after the eruption.

UNESCO adds that the surrounding terrain includes undulating hills, mountains and plains, and that the steep caldera walls form the lake's watersheds.

Green forests grow around the lake today.

The Batak Toba people live here and make a colorful cloth called ulos.

UNESCO says the lake is surrounded by Sumatran forests and provides habitats for many plants and animals. Endemic Toba plants such as andaliman, a spice used in Batak cooking, grow with Toba orchids and pitcher plants in a botanical garden there.

The area is home to the Batak Toba people, known for wooden houses decorated with Gorga carvings in white, red and black, and for ulos, a handwoven cloth.

UNESCO describes Lake Toba as a vital ecological and cultural site surrounded by Sumatran forests. The Eden Park botanical garden features endemic Toba plants such as andaliman, a key spice in Batak cuisine, as well as Toba orchids and pitcher plants.

The geopark is home to the Batak Toba people, whose traditional wooden houses, built on stone foundations without cement, carry Gorga carvings in white, red and black. Their handwoven ulos cloth is dyed with plants such as salaon (Indigofera tinctoria) for blue and sona (Pterocarpus indicus) for red.

Lake Toba is very deep.

Near water, always stay close to your grown-up and wear a life jacket on a boat.

UNESCO gives Lake Toba a maximum depth of 505 meters. The US Centers for Disease Control and Prevention (CDC) says life jackets lower the risk of drowning while boating, and that children should wear them for all activities in and around natural water.

Grown-ups should watch children closely whenever they are near water.

The CDC advises that life jackets reduce the risk of drowning while boating for people of all ages and swimming abilities, that children should use them for all activities in and around natural water, and that adults should supervise children closely even when lifeguards are present.

UNESCO notes the region is prone to tectonic activity, earthquakes and flooding, and says the traditional Batak house style reflects this.