Three Days in Cedar Gap
1Cedar Gap is a mountain town in the Pacific Northwest, about 150 km inland from the ocean. Steep, forested slopes rise on both sides of its valley. The town and its numbers are made up, but they are based on real winter storms in the region. The town's hazards office runs a set of earthquake sensors and also watches slopes that could slide. In January, sixth grader Mattias Ferreira spent three days at the office with geologist Dr. Aiyana Whitcomb for a school project.
2Dr. Whitcomb explained that small earthquakes are felt near Cedar Gap a few times a year, but most of the town's landslides happen during long, heavy winter rain. Water that soaks into the soil makes a slope heavier and weaker. In a cold storm, snow piles up on the slopes instead of soaking in. The danger is often greatest when heavy rain falls on deep snow, because melting snow adds its water to the rain.
3An air mass is a huge body of air with about the same temperature and humidity throughout. It takes on the conditions of the place where it forms. In winter, air that forms over the cold interior of Canada is usually cold and dry. Air that forms over the warm Pacific Ocean far to the southwest is usually mild and very humid. The dew point shows how much water vapor the air holds: the higher the dew point, the more water vapor. When humid air is pushed up the mountain slopes, it cools, and much of its water vapor condenses into clouds and falls as rain or snow.
4The office has a weather station on the valley floor, at 600 m, and another on Lookout Ridge, at 1,500 m. A sensor buried in the old slide slope above Fir Street measures how much of the soil is water. When it reads 40% or more, the office warns the families who live below the slope. Mattias copied the readings every 12 hours, from Monday morning to Thursday morning.