2. Mt. St. Helens Fact file! Mount St. Helens is found in the Cascade Range, along the west coast of Washington State, USA. The volcano is 30,000 years old . Mount St Helens erupts violently about once every 3,000 to 4,000 years . The volcano erupted most recently at 08.32am on 18th May 1980 . Mt. St. Helens is in the Rockies National Park. It is a popular location for outdoor activities such as walking and skiing. Tourism is an important way local people can make money. We love hiking here, don’t we Boo Boo! As long as it’s not erupting… Mt. St. Helens Background MAIN PAGE

3. I’m Ranger Smith and I’m going to show you why Mt. St. Helens erupted… The build up of magma forced the side of the volcano to bulge outwards. The force of the magma was growing at a rate of 1.5m a day. Here we can see that magma began to make its way to the surface. 1 2 Eventually an earthquake (5 on richter scale) at 8.32 am on 18 th May 1980 meant that bulge collapsed and a deadly pyroclastic flow exploded out of the side of the volcano. 3 Mt St Helens is located on a DESTRUCTIVE plate boundary where a continental plate (North American) meets an oceanic plate (Juan de Fuca). 1 2 3 Why did Mt. St. Helens erupt? MAIN PAGE

4. The first time we thought the volcano was awakening after 123 years was when, on the 20 th March, a moderate earthquake (4.1 on the Richter scale) under the volcano was recorded on the SEISMOMETER . This was the result of rising magma. Seismometers measure the vibrations caused by movements in the earths crust . On March 30th there were a record 79 earthquakes recorded on the mountain! Animals were acting strangely before the earthquake. Dogs were howling, and fish were seen jumping in the rivers. We were also busy measuring volcanic emissions (gases) at the crater as these increase before an eruption. We were shocked when there was a small eruption of steam and ash. Our geologist was monitoring the volcanoes shape . The shape often changes as magma gathering in the magma chamber causes swelling of the slopes. Tiltmeters measure these changes. It was swelling and swelling by 1.5m a day!! Prediction More… MAIN PAGE

5. I wonder what they did to try to PREVENT the effects of the earthquakes and volcanic eruption? 25 th March : Following earthquake activity, the mountain was closed to climbers. 27th March : Ash thrown 3 km into the air encouraged sightseers to flock to the area. People were asked to EVACUATE the area. 17 th May : Despite warnings, angry home owners living in the "Red Zone" threatened to break through roadblocks to get to their homes. A convoy 30 car loads of residents enter the restricted zone to gather possessions. April 3 rd : the crater was 1,500 feet wide. Explosions of ash, rock and ice chunks were happening nearly every day. For safety reasons, a " Red Zone " (no-go) and a " Blue Zone " were mapped out around the mountain. Only forestry workers and scientists were allowed in the red zone and to get into the blue zone you needed permission. MAIN PAGE

6. When the volcano erupted there were lots of destructive forces at work. The map above showed what happened in the minutes and hours after the eruption. With the amount of mud and ash falling in the rivers, all the fish were killed. 10 million trees were destroyed and had to be replanted A 25 km2 blast zone around the volcano was an area of total destruction. Every tree in this area was flattened. In total 61 people were killed by the actual eruption and lahars. Mudflows (or lahars) rushed down the mountain sides taking with them millions of logs from the logging camps. Lahars Short Term Effects Pyroclastic flow As the bulge slipped it released a pyroclastic flow – a cloud of super heated steam, gas and ash up to 500 o C and moving at speeds of over 200km. MAIN PAGE

7. Gee Yogi, I wonder what happened later on? Well Boo Boo, it says here there were a number of long term effects… Spirit Lake is normally a chilly 42 degrees, a landslide instantly raised the temperature to nearly 100 degrees . As the mud and rock hit the lake, the intense temperatures and choking ash killed all of the life in the water. Plants and small animals are slowly returning to the water but so far the water is still not able to sustain larger life such as fish. One of the hardest hit industries was logging. Approximately 60,000 acres of trees were lost. Logging camps, buildings and equipment were also lost or damaged. More than 18.4 million trees had to be replanted. Many flights in the area were cancelled as it was too dangerous to fly. The dust meant that engines of all transport (even cars) were affected. Long Term Effects MAIN PAGE

8. An Eyewitness Account by John H Lienhard It was a beautiful Sunday, and I left my home to drive to Oregon, airport. I was booked on Flight No. 271. A few days before, Mt. St. Helens had given an indication of activity with tremors and emitting of gases. Taking this in consideration, I took a window seat on the right side of the aircraft. My purpose being that I wanted to get a good view of the mountain when we flew past. Soon we were directly south of the mountain. The sky was very clear so I had a good view of the mountain. The pilot started to explain to the passengers and said; "There is Mount St. Helens, she has been rather quiet the past few days". I took my eyes off of the mountain and leaned back in my seat. In a matter of seconds the pilot shouted over the speaker: "Everyone look quick, Mount St. Helens is making a spectacular display". At that point, we saw an unbelievable sight. A plume of black ash immediately exploded from the mountain and went straight up into the atmosphere. There appeared to be lightning flashes coming from the crater. At the same moment, it appeared that the westerly part of the mountain exploded and the area and sky went dark with the deep gray to charcoal black ash. The mountain was belching ash and smoke and was very dark and eerie. In a few minutes we were landing at the Portland airport. There was a certain odor in the air that may have been a sulfur odor. I stepped off the plane, shaking with excitement from what I just saw! NEXT Eye Witness Account