Discuss the environmental imapact of Mt. St. Helens tectonic eruption
Mount St Helens is an active volcano, south-western Washington in the Cascade Range. The volcano which had been dormant since 1857, began to show signs of renewed activity in early 1980. On May 18 1980, it erupted with such violence that the top of the mountain was blown off and a cloud of ash and gases was sent to an altitude of 19 km (12 mi).
The blast killed 57 people and destroyed all life in an area of some 180 sq km (70 sq mi); an even wider area was covered with ash and debris. It continues to emit ash and steam intermittently. As a result of the eruption, the mountain’s elevation was decreased from 2,950 m (9,677 ft) to 2,550 m (8,365 ft). A National Volcano Monument was established here in 1982.
May 18th 1980 a kryptodome appeared on the north side of the volcano, before this the volcano hadn’t erupted for over 120 yrs. March 20th an earth quake happened right underneath the volcano signalling an eruption. Unfortunately Lavafrom the last eruption had acted as a plug, and blocked the volcano. Magma was rising at a rate of six feet a day, casing a bulge on the side of the mountain (Kryptodome). Scientists were using GPS (global Positioning satellites) to monitor the Volcano. March 31st state of emergency announced, 20m exclusion zone was placed around the volcano.
May 18th the Kryptodome receded 300 feet, at 8:32 a last surge of magma caused a 5.1 Richter scale earthquake. The earthquake caused an avalanche which took the side of the mountain out; this was followed by a horizontal blast which moved at 700 mph. The blast cloud ripped through the forest, and reached Spirit Lake filling it with debris. Two minutes from the start of the blast no signs of stopping. Landslide was biggest ever recorded.
The satellite picture shows the damage of the volcano’s blast to the forest. Thousands of trees up to 13km around the volcano were destroyed they were incinerated from the Pyroclastic flow. From there 30km around the volcano were blown down trees, that had to be salvaged for timber. Following that was the seared/scorched trees, which would take years to recover. The blast has caused severe damage to the vegetation around Mount St. Helens which will last for years to come.
When Mount St. Helens erupted it caused massive damage to the climax community vegetation of the region mainly coniferous woodlands. With whole areas now covered in bare rock vegetation succession has now got to take place again. Starting with the pioneer communities having to reconalize the area. Vegetation succession takes years to finish with the Climax vegetation. The environmental impact of this is tremendous. However with this area it has patchy areas of growth because only the north side was affected by the blast. Half the are has a climax community and the other side has just started pioneer community.
The hydrological effect of the eruption was localised to Spirit Lake and the North and South Toutle River. Spirit Lake layer directly in the blast zone the brown earth surrounding the lake is the scorched earth. From the graph he immediate impact of the Pyroclastic flow, when it filled the Lake with debris form the Volcano it dramatically changed the temperature of the lake. Which in turn effected the vegetation and wild life in the Lake. The vegetation and wildlife was boiled alive. For the river to recover form this is would take years, to help along the process the ecologists of the area suggested that the fisheries department of the United States should replace the fish and plant new vegetation to help succession. The advice was acted upon and vegetation and wild life were added, causing a Plagioclimax community.
The main reason a lot of the devastation was caused was by the Lahars and Pyroclastic flows, the ground around the volcano is low lying land. If you look at the diagram on the right you can see the red represents highest ground and the purple is low lying ground. Because of this at the bottom of the Volcano is low lying ground and Lahars and Pyroclastic flows hug the ground. Causing the Pyroclastic flow to be directed down the slope on the north side because it is all low lying ground.
The volcano only caused one global impact, the atmospheric dust cloud. Mount St. Helens before the eruption was 9,677 feet. After the eruption it dropped to 8,365 feet. The ash cloud reached over 15km into the sky, by two weeks it had encircled the entire planet. All around the world day had turned to night, this was a global impact that lasted for weeks.
The lasting impact of the eruption will always been seen at Mt. St. Helens. As pic. 5 shows there has been a massive scare left on the Vlocano forever.