Question: On what date did the 1980 eruption of Mount St. Helens, in which "Crater Glacier" was formed, occur?

Context articles: Seaquest State Park
Toutle, Washington
Helenite
St. Helens (film)
1980 eruption of Mount St. Helens
Harry Randall Truman
2004–08 volcanic activity of Mount St. Helens
Crater Glacier
Spirit Lake (Washington)
Silver Lake, Washington

Seaquest State Park is a publicly owned recreation area located on the western flank of Silver Lake in Cowlitz County, Washington.
 The 475 acre state park is home to the Mount St. Helens Visitor Center, which offers displays on the Mount St. Helens volcanic eruption of 1980.
 Mount St. Helens itself is approximately 44 mi east of the park.
Toutle is an unincorporated community in Cowlitz County, Washington.
 Toutle is located 10 mi east of Castle Rock along Washington State Route 504, which is also known as the Spirit Lake Memorial Highway.
 The Toutle community, similar to Toutle River, takes its name from the "Hullooetell", a band of the Skillot - a Chinookan tribe.
 The Toutle community is part of the Toutle Lake School District, a K-12 school district of about 600 students.
 Toutle is near Mount St. Helens and the Mount St. Helens National Volcanic Monument, which lies at the end of the Spirit Lake Memorial Highway.
 The eruption of Mount St. Helens on May 18, 1980 was the deadliest and most economically destructive volcanic event in the history of the United States.
Helenite, also known as Mount St. Helens obsidian, emerald obsidianite, and ruby obsidianite, is an artificial glass made from the fused volcanic rock dust from Mount St. Helens and marketed as a gemstone.
 Helenite was first created accidentally after the eruption of Mount St. Helens in 1980.
 Workers from the Weyerhaeuser Timber Company were attempting to salvage equipment damaged after the volcanic eruption.
 Using acetylene torches, they noticed that the intense heat was melting the nearby volcanic ash and rock and turning it a greenish color.
 The silica, aluminium, iron, and trace amounts of chromium and copper present in the rocks and ash in the area, combined with the heat of the torches, transformed the volcanic particles into a compound that would be later commercially replicated as helenite.
St. Helens, aka St. Helens, Killer Volcano, is a 1981 made for cable HBO film directed by Ernest Pintoff and starring David Huffman, Art Carney, Cassie Yates, and Albert Salmi.
 The film centers on the events leading up to the cataclysmic 1980 eruption of Mount St. Helens in Washington state, with the story beginning on the day volcanic activity started on March 20, 1980, and ending on the day of the eruption: May 18, 1980.
On May 18, 1980, a major volcanic eruption occurred at Mount St. Helens, a volcano located in Skamania County, in the state of Washington, United States.
 The eruption (a VEI 5 event) was the only significant volcanic eruption to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California.
 However, it has often been declared as the most disastrous volcanic eruption in United States history.
 The eruption was preceded by a two-month series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain's north slope.
Harry Randall Truman (October 30, 1896 – May 18, 1980) was a resident of the U.S. state of Washington who lived on Mount St. Helens.
 He came to brief fame in the months preceding the volcano's 1980 eruption after he stubbornly refused to leave his home despite evacuation orders, and he is presumed to have been killed in the eruption.
 He was the owner and caretaker of Mount St. Helens Lodge at Spirit Lake, located at the south end of Spirit Lake at the foot of the mountain in the danger zone at the time of the eruption.
The 2004–2008 volcanic activity of Mount St. Helens, Washington, United States has been documented as a continuous eruption in the form of gradual extrusion of magma.
 Starting in October 2004 and ceasing in January 2008, a new lava dome was built up.
 The new dome did not rise above the crater created by the 1980 eruption of Mount St. Helens.
The Crater Glacier (also known as Tulutson Glacier) is a geologically young glacier that is located on Mount St. Helens, in the U.S. state of Washington.
 The glacier formed after the 1980 Eruption and due to its location, the body of ice grew rapidly, unknown to the public for nearly 20 years.
 The glacier once contained ice caves in the smooth ice before the 2004-2008 volcanic activity.
 The growth of the lava dome and volcanic eruptions from 2004 to 2008 significantly altered the appearance of the glacier.
 In the same time period, several agencies decided to put an official name on the glacier which, at first, was Tulutson Glacier.
 A later decision made Crater Glacier the official glacier name.
 Despite the volcanic activity, the glacier continued to advance and by mid-2008, the glacier completely encircled the lava domes.
 In addition, new glaciers (rock or ice) have formed around Crater Glacier as well.
Spirit Lake is a lake north of Mount St. Helens in Washington State.
 The lake was a popular tourist destination for many years until the 1980 eruption of Mount St. Helens.
 Prior to 1980, there were six camps on the shore of Spirit Lake: a Boy Scout camp (Columbia Pacific Council), a Girl Scout camp, two YMCA camps (Longview YMCA camp Loowit, and Portland YMCA camp), Harmony Fall Lodge, and another for the general public.
 There were also a number of lodges catering to visitors, including Spirit Lake Lodge and Mt. St. Helens Lodge; the latter was inhabited by Harry R. Truman, who became one of the volcano's victims.
Silver Lake is an unincorporated community in Cowlitz County, Washington.
 Silver Lake is located 6 mi east of Castle Rock along Washington State Route 504, which is also known as the Spirit Lake Memorial Highway.
 The Silver Lake community takes its name from the lake of the same name, which it lies on the northwest shore of.
 The Silver Lake community is part of the Toutle Lake School District, a K-12 school district of about 600 students.
 Silver Lake is near Mount St. Helens and the Mount St. Helens National Volcanic Monument, which lies at the end of the Spirit Lake Memorial Highway.
 The eruption of Mount St. Helens on May 18, 1980 was the deadliest and most economically destructive volcanic event in the history of the United States.
 The WDFW has planted Grass Carp in this lake, however it is illegal to fish for or retain grass carp.