On August 27, 1883, just after 10 a. m, the eruption of the Krakatoa volcano in Indonesia made the loudest sound known to history. It sent sound waves around the world four times and could be heard 3,000 miles away on the island of Rodrigues in the Indian Ocean. That, for the purpose of comparison, is the same as Californians hearing a noise made in New York. In Rodrigues, as in other faraway places, the noise was taken to be cannon(大炮)fire. In Western Australia, 2,000 miles away, people thought war had erupted.

The sound was so powerful that it ruptured(使破裂) the eardrums(鼓膜) of people working on a British ship 40 miles from the eruption. “This is so surprisingly loud,” writer Aatish Bhatia noted in Discover magazine post.

The Krakatoa eruption was one of history’s deadliest natural disasters. More than 36, 400 people died, from lava flows that raced at 60 miles per hour and tsunamis that reached a height of 120 feet and destroyed some 165 coastal villages.

Volcanic matter thrown into the air caused sunsets so strange that people in New York, Connecticut and other places called the fire department, fearing fires had broken out. In the year following the eruption, the average temperature around the world fell by 1.2 degrees Celsius (℃), and the earth remained unusually cool for about five more years.

Little was left of Krakatoa after the eruption. In 1927, a volcanic island known as Anak Krakatoa was formed at the site of the big eruption. It is an active volcano. An eruption in December 2018 caused a tsunami that killed more than 400 people.

Spending time in nature has been known to positively impact mental health for some time now, but even greenery planted along a sidewalk line can be beneficial.

Mental health experts have long believed the health benefits of spending time in nature and there’re many related studies. A team of German researchers studied the long-term connection between living in an urban area where there are fewer green spaces and levels of depression. To understand the impact of being near a green space—specifically, trees planted along neighborhood sidewalks —they examined data from 10,000 residents of Leipzig, the most populated city in Saxony, Germany. Researchers assessed the number and type of street trees, how close they were planted to homes, and the number of drugs residents take to treat depression.

In addition to their closeness to green spaces, researchers also took into account the age, employment status, gender, and body weight of each of the participants. They found that trees located within 100 meters of the home were associated with a lower risk of being given antidepressants(抗抑郁药)，particularly in poor or unimportant neighborhoods. As these populations are usually at a greater risk of being given antidepressants in Germany, the findings prove just how beneficial green spaces in urban areas can be for improving mental health.

“Our findings suggest that street trees— a publicly accessible form of urban green spaces taking up a small area— can help close the gap in health inequalities between economically different social groups,” says Dr. Melissa Marselle, lead author of the study. “This is good news because street trees are relatively easy to achieve and their number can be increased without much planning effort.”

In addition to the mental health benefits for humans, planting more trees is also good for the environment. “Adding street trees in residential urban areas is a nature-based solution that may not only promote mental health, but also contribute to biodiversity conservation and mitigating climate change, says senior author Professor Aletta Bonn.