How to Plant on Top of an Ancient Lahar

The lahar from Mt. Raupehu flowing under a bridge in New Zealand in March 2007.

A lahar is a dangerous combination of rocks, mud and acidic water that flows from the slopes of a volcano. In New Zealand, Mount Ruapehu produces lahars on a regular basis--45 since a disasterous mudflow in 1953 killed 151 people. In the United States, Mt. St. Helens produced a lahar that moved up to 125 miles per hour, killing 57 people. Despite the danger of the volano, most ancient lahars erode and decompose into some of the most fertile soil in the world.

Things You'll Need

• Shovel
• Rake
• Compost
• Seeds
• Soaker hose
• Mulch

Instructions

1. Select a garden site that receives at least six hours of direct sunlight daily. If the site does not drain well, consider building raised beds.

2. Take a sample of soil to your local agricultural extension office for testing. Depending on how long ago the lahar occurred, the soil may still be very acidic due to the volcanic ash. Add wood ash or lime, if necessary, to lower the acidity of the soil.

3. Dig the garden with a shovel, removing all grass, roots and as many rocks as possible. Alternatively, till with a rototiller and rake out the grass and rocks till the soil is smooth. Depending on how many centuries since the last lahar and local conditions, the landscape may have weathered to fertile soil or is still filled with granite rocks. Use the rocks to border the garden.

4. Add 3 to 4 inches of compost. Rake evenly over the soil, then dig into the garden. Rake again, pulling the soil into mounded rows.

5. Plant the seeds according to the package directions. Water gently so the seeds are not dislodged.

6. Roll out the soaker hose and wind it between the rows. Water in the early morning, keeping the soil moist until the seeds sprout.

7. Add 3 to 4 inches of mulch, keeping it 3 inches from the seeds. Mulch helps keep the mounded rows moist while the seeds sprout.

Tips & Warnings

• Consult with your local agricultural extension office for information on soil composition, amendments and plants that thrive in your area.

• Wear gloves and sunscreen when gardening. Wear safety glasses when tilling the soil.

• The soil over the lahar will vary, depending on climate, altitude, native plants and the age of the lahar.

References

• "CBC News"; Mud Flow Rushes Down New Zealand Volcano; The Associated Press; March 2007
• "Mt. St. Helens"; The Victims of the Eruption; Valerie A. Smith; June 2006
• "Washington State University Extension"; Soils of the Puget Sound Area; Craig Cogger
• Pierce County Washington: Chapter Fifteen--Physical Features
• "Horticulture & Home Pest News"; How to Change Your Soil's pH; Eldon Everhart; April 1994

Resources

• "Fox News"; Mount St. Helens Still Recovering, 30 Years Later; Andrea Thompson; May 2010
• CVO: The Plus Side of Volcanoes Fertile Soil
• The Volcano Information Center: Soils From Volcanoes