Lessons in catastrophe

The eruptions last autumn of Mount St. Helens in Washington state, in the USA, reminded the media of the remarkable event almost 25 years ago. Up to May 1980, the volcano stood high above a lovely landscape, a beauty spot with huge forests and a variety of flora and fauna surrounding Spirit Lake.

After some months of rumblings indicating that the sleeper was awaking, Mt. St. Helens exploded at 8.32 am on May 18 1980. It had been preceded by an earthquake (5.1 on the Richter scale) on May 12, and then there were nine hours of explosions on May 18, estimated as equivalent to at least 20,000 atomic bombs. The top 1,300 feet of the mountain were blown away, causing a cloud of dust 95 miles in diameter and 30 miles high!

Within two hours it had spread 150 miles eastwards, covering five states and causing street lights to come on prematurely. Some of the ash was detected 950 miles away. The steam blast demolished enough trees to build 600,000 homes up to five miles away within ten minutes. Some of these trees had been eight feet in diameter and 150 feet tall!

The lateral air blast was measured to be 500 degrees Celsius and travelled at 200 m.p.h. It threw boulders the size of a house ten miles away. It scoured ridges and levelled forests for over 15 miles. The trees were stripped of leaves, twigs and smaller branches. Many were ripped up from their roots and lay scattered around the area. Subsequent steam blasts scoured pits in the pumice, one being measured at 2,300 x 1,000 feet and 125 feet deep.

Rock and ice fell into Spirit Lake making an enormous wave up to 850 feet high, and this scoured the northern slopes, washing them into the lake. Over 300 feet of debris was deposited in the lake, raising its level by 200 feet compared with the previous depth. Trees close to the lake were washed into it.

Mudflow blocked the rivers, washed away bridges and even raised a boulder 17 feet in diameter, through 30 feet onto a road. It was estimated to weigh 37 tonnes. The ash deposit was up to 500 feet deep in some places and covered an area of over 200 square miles. Not only had the Mount itself changed dramatically, but so had the environment. Some people described it as looking like the surface of the moon. But this was only the first of three significant events.

Not yet finished!

The awakened giant had not finished speaking. A month later on June 12, there was a pyroclastic flow from the volcano. Two years later on March 19 1982 there was a further eruption producing an extensive mudflow.

The pyroclastic flow travelled across the first deposit at 100 m.p.h., depositing 25 feet of rock in one evening. What was remarkable was the process of stratification that occurred. In spite of the speed of travel, the rocks in the flow were finely sorted giving very clear and precise lamination. Though the drama of the eruption is frequently shown in educational programmes, this amazing process of stratification is not, and yet it is an invaluable aid to interpreting geological history. The later mudflow travelled at 40 m.p.h. forming a final covering to the episode. Within five years, the sediments had solidified and hardened.

Canyons

One of the sights of this region today is the existence of canyons. The whole is reminiscent of the Grand Canyon, but is a fortieth of the size. As mentioned before, the rivers were choked by ash deposits. This caused concern among environmentalists because it prevented normal drainage from the lake. It was generally considered (as argued concerning the Colorado river in the Grand Canyon) that drainage gullies were formed very slowly as rivers eroded them. That did not happen here. When the mudflow occurred in 1982, it filled a big steam explosion pit like the one described earlier. The mudflow then broke through this pit and gouged out a 140 feet channel through the debris. Military engineers drained more water from the lake over two years, by pumping out more water and forming another canyon. The present river systems exist as a result of catastrophic erosion of the canyons, and were not the cause of canyon formation.

Back to the lake!

But let us return to Spirit Lake. Remarkable things have been happening here. Over 1,000,000 tree logs had been washed into the lake, obscuring most of its surface. As the trunks became water-logged, they begin to tilt into a vertical position and then slowly sink. Underwater investigations three years after the eruption showed that the light debris from the trees (bark, branches, leaves, etc.) had sunk to the bottom, and, under the effect of pressure, been converted to peat. This was in contrast to the usual timescale quoted (thousands of years) for peat formation.

The trees themselves have sunk at differing rates, with half of them now at the bottom of the lake in an upright position. Because there is sediment settling in the lake even today, the trees are based in different layers of sediment. This is the type of formation found in fossilised forests, and historically would have been considered chronologically separate forests. In Spirit Lake they were swept into this position and sank at different times due to physical differences.

Speed of recovery

One other amazing result of this catastrophe has been the speed of recovery. After such a heat-searing event, one would have expected the return to an ecologically-balanced environment to be slow. Instead, the ash appears to be a good fertiliser and is even sold for that purpose. Flora and fauna have returned. One researcher commented on the Spirit Lake as having a 'blizzard of invertebrates'. This recovery has been described as the 'second eruption' and 'nature on fast forward'. One of the first plants to appear in the area was the lupin. This is very significant as its roots have a symbiotic relationship with rhizobial bacteria and produce nitrogen which fertilises the soil, preparing it for other vegetation. Interestingly, their spread is checked by the arrival of moths and their caterpillars which feed on them. This is vital to the spread of new flora, as the lupins, if allowed uncontrolled growth, would prevent the establishment of new plants. So the new cycle of ecological growth begins.

Over-arching providence

Why is this of interest to readers of EN? It reminds us of the power of catastrophe. We see how devastating is the power of water and it reminds us of the flood in the days of Noah and how disastrous that was. We see that, even in these volcanic conditions, rocks are laid fast and can be host to a rapid recovery. How much more so in a water-based deposit which, presumably, must have been more fertile - not to mention the over-arching providence of God.

It also reminds us, as Peter describes in 2 Peter 3, of the final catastrophe when God will destroy this present world. Mount St. Helens is a gospel warning. The early rumblings of the mountain meant that geologists warned people to leave. Most did; a few remained. One was a man called Harry Truman. He had lived there all his life; he knew the mountain better than any. There was no way he was going to leave. May 18 1980 was the day he died.

God has issued many warnings to the unsaved. The time of his patience will run out. These days are, as Peter points out, days of God's grace. Let Mount St. Helens speak to our generation. 'Come and see the works of the Lord, what desolations he has made in the earth' (Psalm 46.8).

Lessons in catastrophe

Not yet finished!

Canyons

Back to the lake!

Speed of recovery

Over-arching providence

John Peet

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