objects, especially iron-nickel meteors and other types descending at a steep angle, can explode close to ground level or even directly impact onto land or sea. In the U.S. State of Arizona, the Meteor Crater (officially named Barringer Crater) formed in a fraction of a second as nearly 160 million tonnes of limestone and bedrock were uplifted, creating its crater rim on formerly flat terrain. The asteroid that produced the Barringer Crater was only about in size; however it impacted the ground at a velocity of and struck with an impact energy of —about 625 times greater than the bomb that destroyed the city of Hiroshima during World War II. Tsunamis can also occur after a medium-sized or larger asteroid impacts an ocean surface or other large body of water. The probability of a mid-sized asteroid (similar to the one that destroyed the Tunguska River area of Russia in 1908) hitting Earth during the 21st century has been estimated at 30%. Since the Earth is currently more populated than in previous eras, there is a greater risk of large casualties arising from a mid-sized asteroid impact. However, as of the early 2010s, only about a half of one per cent of Tunguska-type NEOs had been located by astronomers using ground-based telescope surveys. The need for an asteroid detection program has been compared to the need for monsoon, typhoon, and hurricane preparedness. As the B612 Foundation and other organizations have publicly noted, of the different types of natural catastrophes that can occur on our planet, asteroid strikes are the only one that the world now has the technical capability to prevent. B612 is one of several organizations to propose detailed dynamic surveys of NEOs and preventative measures such as asteroid deflection. Other groups include Chinese researchers, NASA in the United States, NEOShield in Europe, as well as the international Spaceguard Foundation. In December 2009 Roscosmos Russian Federal Space Agency director Anatoly Perminov proposed a deflection mission to the asteroid 99942 Apophis, which at the time had been thought to pose a risk of collision with Earth. Asteroid deflection workshop The Foundation evolved from an informal one-day workshop on asteroid deflection strategies during October 2001, organized by Dutch astrophysicist Piet Hut along with physicist and then-U.S. astronaut Ed Lu, presented at NASA's Johnson Space Center in Houston, Texas. Twenty researchers participated, principally from various NASA facilities plus the non-profit Southwest Research Institute,