Eyjafjallajokull – and how local eruptions can have broader-scale impacts

Today’s news carried this interesting article about the Eyjafjallajokull volcano in Iceland. (Typing the word Eyjafjallajokull is great fun–and and trying to correctly say it even more so.)

In certain cases, volcanic eruptions spew large amounts of sulfur dioxide into the atmosphere, where it forms an aerosol, essentially a suspension of sulfate particles in a gas. These aerosols can stay high in Earth’s atmosphere, often for two to three years, and, if the eruption is large enough, will spread out over an entire hemisphere or even the globe. Aerosols absorb some of the longer wavelength terrestrial radiation from Earth, warming the upper atmosphere. They also reflect incoming sunlight back to space, leading to cooler surface temperatures. In this way, a localized volcanic eruption can affect climate worldwide–past volcanic events have led to colder seasons, freezing at lower latitudes, and crop failures. Learn more by reading this story of how scientists have used observations and models to fit the pieces of the volcano-climate puzzle together.

Melting Snow and Rising Rivers

This map of snow water equivalent shows the amount of water contained in the snowpack–essentially, the depth of water released if the entire snowpack was melted instantaneously.

snow water equivalent

The map comes from the National Operational Hydrologic Remote Sensing Center, which also provides information about snow depth and other snow-related variables.

Snow water equivalent provides useful information for water supply (and things like soil moisture for agriculture and other land uses) as well as for flood forecasting. It’s an important number to watch during the spring months, particularly along the Nebraska-Iowa and North Dakota/South Dakota-Minnesota borders.

In these areas, the snow is melting (at last!). But there’s been a lot of snow over much of the upper midwest this winter, and it’s melting quickly. That can mean lots of surface runoff, especially in areas of deep frost, which can cause localized flooding. Eventually, this runoff makes it into the rivers, where high water levels and potential ice jamming can lead to rivers spilling over banks and levees, resulting in property damage, and in some cases, potential loss of life.

The National Weather Service has a flood safety website to help you learn about the flood danger in your particular area and review safety tips. Understanding the danger as well as the actions you can take will help you be better prepared if or when flooding does occur.

Today’s Instructional Lesson: Seiches

A seiche is an oscillation associated with a standing wave that occurs in an enclosed or partially enclosed body of water, resulting from seismic activity or meteorological effects.

graphic of wind-driven seiche
Click to view this University of Wisconsin Sea Grant Institute animation of a wind-driven seiche. Seiches are not uncommon phenomena on the Great Lakes and adjacent bays and rivers.

Seiches have been observed on lakes, reservoirs, ponds, rivers, and even swimming pools. You can create your own seiche in your bathtub, just by rocking back and forth. At the right frequency, you can set up an oscillation–essentially a small-scale seiche–that allows the waves to grow until they overflow the bath.

A similar “sloshing”–in this case a seismic seiche–was observed on Saturday, February 27, on Lake Pontchartrain in Louisiana, caused by an earthquake 4,700 miles away off the coast of Maule, Chile. Lake Pontchartrain sits on the Mississippi Delta, which contains a deep layer of surface sediments. Seismic waves can resonate through this sediment more easily than through more firm surface types, making the Gulf region particularly sensitive to earthquake-induced seiches. The seiche affecting Lake Pontchartrain occurred 11 minutes after the 8.8 magnitude Chilean earthquake and resulted in water levels about 6 inches higher than the predicted tides.

Want the video version? Derek Kevra at WWLTV has a great explanation of the quake and resulting seiche here. And if you want to learn more about seiches in history, check out this page from the USGS Earthquake Hazards program.

Sunrise, Sunset, and Moving Swiftly Through the Days

A new month in a new year and it’s gone by far too quickly. I thought I’d close out the lengthening days of January by sharing some interesting sources of information. The pick for today is the NOAA Sunrise/Sunset Calculator, developed by some talented former colleagues. It is a resource used by people in all walks of life—from scientists and sky watchers to film makers and event planners—and a great way to explore what’s going on in terms of the number of hours of daylight received in a day.

According to the calculator, at 40 degrees latitude in the approximate middle of the mountain time zone, the apparent sunrise on January 31 is 7:09 a.m. and apparent sunset is 5:19 p.m. What’s “apparent” sunrise, you ask? Let’s use this graphic from the solar calculator Help Guide (really guys, great work putting this resource together!) to illustrate:

schematic showing reflection of visible light by atmosphere
Gases in Earth\’s atmosphere refract visible light from the Sun.

Earth’s atmosphere refracts (or bends) incoming light from the Sun. Because of that refraction, we see the sun “rise” shortly before it actually crosses the horizon. Likewise, we see the setting sun for a short time after the sun has actually “sunk” below the horizon at the end of a day. (If this part sounds like desperation from a person eager for any at all additional daylight, well, consider that mid-latitude winters sometimes just seem…long.) Apparent sunrise and sunset times are different than actual sunrise and sunset times, adding just that little bit of additional time to the number of hours of daylight in a day.

The nice thing about the end of January sunrise and sunset times is how they differ from the dark, dark days of December. Did we talk about the solstice on December 21? On that day, the apparent sunrise was at 7:18 a.m. but the sun was gone a full 40 minutes earlier, at 4:39 p.m. For those of us desperate enough to grab those few minutes based on apparent sunrise and sunset, 40 minutes seems quite a cause for celebration, or at least acknowledgment. Go ahead, play with sunrise and sunset times for your location, and check out what happens at the summer solstice too.