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The Echinus geyser in Yellowstone National Park, USA, has erupted for the first time in six years. Echinus is part of the highly dynamic Norris Basin in Wyoming. Photo: Calvo/VWPics/Universal Images Group via Getty Images.

The eruptions of acidic hot water from the Echinus geyser began last February, repeating every 2-5 hours, lasting about 2-3 minutes with the water column reaching a maximum height of 9 meters. This is the first eruption of Echinus since 2020. Photo: usgs.gov.

Geysers like Echinus are considered rare because the acidic hot water is usually strong enough to destroy the underground silica "pipeline system"—the structure that helps build up pressure. Photo: nps.gov.

However, Echinus retains this structure thanks to its composition of water, which is a suitable ratio of neutral groundwater to acidic gases. This means there isn't enough acid to erode the rock, making Echinus a rare geyser. Photo: MA Bellingham.

According to the U.S. Geological Survey (USGS), Echinus's unique chemical composition gives it its interesting texture and color. The red, orange, and yellow hues of this geyser come from the large amounts of iron, aluminum, and arsenic that accumulate around its jagged edges. Photo: Leo Kohout/Shutterstock.com.

The Echinus geyser is approximately 19 meters wide, with a jagged rim made of silica and surrounded by rocks resembling sea urchins. Photo: oceanlight.com.

The U.S. Geological Survey states that the acidity of Echinus, similar to orange juice or vinegar, is not so strong that it poses no particular danger. However, the water temperature can reach over 93 degrees Celsius. Therefore, visitors should exercise caution when exploring this unique geyser. Photo: marlimillerphoto.com.

Geologists believe that the Echinus geyser was largely inactive, except for occasional eruptions, until 1948. During the 1970s, Echinus erupted regularly with cycles of 40-80 minutes before becoming more violent in the 1980s and 1990s. More violent eruptions sometimes lasted over 90 minutes. (Image: yellowstoneinsider.com)

In the early 2000s, Echinus' eruptions became less frequent and less active as temperatures dropped. From October 18 to November 10, 2017, Echinus erupted continuously for about 2-3 hours at a time. After that, activity subsided again, with only one eruption in January 2018 and 2019, and two in December 2020. Photo: yellowstoneinsider.com.

Experts believe that the current eruption of the Echinus geyser is quite similar to the period when it reactivated in 2017. Photo: yellowstoneinsider.com.

Rare hot spring geysers in the US are working again.

The Echinus geyser at Yellowstone has erupted again after six years, creating a column of highly acidic hot water with temperatures close to 100 degrees Celsius, attracting many visitors.