Please answer the following question: By what specific date had a 16,000-foot-long eastward-trending fracture system developed across the summit area?  Answer the above question based on the context below:  Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980. Several small earthquakes, beginning on March 15, indicated that magma may have begun moving below the volcano. On March 20, at 3:45 p.m. Pacific Standard Time (all times will be in PST or PDT), a shallow magnitude 4.2 earthquake centered below the volcano's north flank, signaled the volcano's violent return from 123 years of hibernation. A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale. A total of 174 shocks of magnitude 2.6 or greater were recorded during those two days. Shocks of magnitude 3.2 or greater occurred at a slightly increasing rate during April and May with five earthquakes of magnitude 4 or above per day in early April, and eight per day the week before May 18. Initially there was no direct sign of eruption, but small earthquake-induced avalanches of snow and ice were reported from aerial observations. At 12:36 p.m. on March 27, phreatic eruptions (explosions of steam caused by magma suddenly heating groundwater) ejected and smashed rock from within the old summit crater, excavating a new crater 250 feet (75 m) wide, and sending an ash column about 7,000 feet (2.1 km) into the air. By this date a 16,000-foot-long (3.0 mi; 4.9 km) eastward-trending fracture system had also developed across the summit area. This was followed by more earthquake swarms and a series of steam explosions that sent ash 10,000 to 11,000 feet (3,000 to 3,400 m) above their vent. Most of this ash fell between three and twelve miles (5 and 19 km) from its vent, but some was carried 150 miles (240 km) south to Bend, Oregon, or 285 miles (460 km) east to Spokane, Washington.
Answer:
March 27