Why Did This Mysterious Crack Appear in Michigan?

A strange and sudden buckling of the earth in Michigan five years ago is now being explained as a limestone bulge. Continue reading →

A strange and sudden buckling of the earth in Michigan five years ago is now being explained as a limestone bulge, researchers reported Monday.

The upheaved rock and soil was discovered after a deep boom thundered through the forest near Birch Creek on Michigan's Upper Peninsula, north of Menominee. The sound shook nearby homes with the strength of a magnitude-1 earthquake on Oct. 4, 2010, at about 8:30 a.m. Central time, residents said at the time. The next day, locals discovered a long crack atop a narrow ridge.

The crack was 360 feet (110 meters) long and about 5 feet (1.7 m) deep; and the ridge was nearly 7 feet (2 m) high and about 30 feet (9 m) wide at its largest point. Tilted trees leaned away from the crack at about 14 degrees on either side - proof the ridge was new. Torn roots stretched for their former companions, now stranded on the other side of the crack. [See Photos of the Weird Crack and Uprooted Trees]

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"It was interesting to see that the crack seemed to ignore the roots," said senior study author Wayne Pennington, dean of the College of Engineering at Michigan Technology University in Houghton. "The forces were stronger than the roots."

Based on a seismic study, the most likely explanation for the ridge is a pop-up in the upper layers of limestone beneath the clay soil, Pennington and his co-authors, all MTU students, concluded in a study published in the journal Seismological Research Letters.

If I had a hammer Even though the researchers can't say for sure what caused the pop-up, they now have a better picture of what happened underground.

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The teams surveyed the underground rock by creating sound waves with a sledgehammer. The researchers slammed a sledgehammer into a metal ball sitting on the ground, and tracked how the waves passed through the soil and rock layers below. The analysis revealed a sharp buckle in the limestone below the crack.

That picture suggested the bedrock limestone violently heaved upward when the pop-up appeared, displacing the overlying clay layer. The clay soil is about 5 feet (1.5 m) deep along the ridge. The crack resulted from the stretching of the surface clay as it bent upward, much as a crack forms in the top of a loaf of bread as the dough rises.

The survey confirms there is no earthquake fault underlying the ridge. Besides, it would take a tremendous earthquake to move the rock and soil several vertical feet, Pennington said.

Pop goes the bedrock Pop-ups are common in quarries in eastern North America, where rock removal releases pent-up strain in the underlying rocks. Pop-ups also appear after glaciers retreat; however, the last glaciers retreated from Menominee 11,000 years ago, and there is no quarrying in the area.

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Rocks in the area are squeezed by plate tectonics, the researchers said. The Midwest is under pressure from squeezing coming from the West Coast and the East Coast.

Yet the region is not experiencing increased stress that would result in future larger earthquakes, Pennington added. The pop-up appeared in the uppermost bedrock, whereas large earthquakes strike miles deep. There have been two moderate earthquakes in Michigan since 2010, which were in different areas and unrelated to the crack, the scientists said.

One final clue was the loss, to lightning, of a giant white pine tree in the week before the crack appeared. "The timing is remarkable, and it leads us to be suspicious, but the tree weighed less than a fully loaded dump truck," Pennington told Live Science.

"The earth is still full of surprises," Pennington said. "It's just a little surprise, but it's still interesting and we're always learning more."

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The mystery of why leaves take such different shapes is closer to being solved thanks to a new mathematical model that looks at the problem from the perspective of leaf veins. Since plants suck up more of the greenhouse gas carbon dioxide than anything else on the planet, understanding leaf veins is an important part of grappling with the global carbon budget puzzle.

"Across the world leaves take a very large amount of carbon out of the atmosphere each year," said Ben Blonder a doctoral student at the University of Arizona. Leaves absorb more than the oceans and about 10 times more than the amount humans put into the atmosphere. "To understand the carbon flux, you have to understand how leaves work, Blonder told Discovery News. "But not all leaves work the same."

There are basically three things at play in the workings of a leaf: the amount of carbon required to make it, how long the leaf lives and how fast or slow it processes sunlight -- or its rate of photosynthesis. These factors combine in different ways in different plants in different environments to create an incredible diversity of leaf shapes and structures. And veins are the basis of it all. "The really surprising thing is that these things relate to each other in ways that don't change across the globe," Blonder said.

Blonder developed a mathematical model to predict how leaves are balancing these three factors to best serve a plant, using three properties seen in the vein networks of leaves: density, distance between veins and the number regions of smaller veins that resemble capillaries in humans, referred to in this case as loops.

Vein density is a sign of how much a leaf has invested in the network. The distance between the veins is a measure of how well the veins are keeping the leaf supplied with water and nutrients. The number of loops shows how resilient a leaf is and is related to how long a leaf lives, since loops provide ways to re-route supplies in the case a leaf gets damaged.

Veins tell you a lot about a plant. For example, if a plant opens its leaf pores, called stomata, to absorb more carbon dioxide for photosynthesis, the leaf also loses a lot of water to evaporation. That requires lots of plumbing in the leaves to pipe in the water. That, in turn, means lots of big veins. If a plant requires lots of water all the time, it could favor certain geometrical arrangements of veins, which starts to suggest overall leaf shapes. So it's the veins -- the skeleton of the leaf -- which determine whether you will have a classic maple shape or a blade-like willow.

"Veins do all sorts of things," said Blonder. They provide structural support, resist damage, transport nutrients and even help send chemical signals to the plant, similar to nerves in an animal. "There are trade-offs for leaf patterns," he added. "What we've been able to do is synthesize these things so they all make sense on one big picture."

Blonder tested his model -- predicting relationships among photosynthesis rates, leaf lifespan, carbon cost and even nitrogen costs -- on more than 2,500 species worldwide. It worked. Then he and undergraduates assistants Lindsey Parker, Jackie Bezinson and David Cahler tested 25 leaves from the University of Arizona campus. Their initial results suggest the model works on a local scale, although they are expanding their tests to study leaves from species at the Rocky Mountain Biological Laboratory in Colorado. Blonder and his students have published their work on veins in the journal Ecology Letters.

Ultimately, a good understanding of leaves will become incorporated into climate models. This can help not only balance the carbon budget, but also predict evaporation rates and other weather and climate-related matters that are heavily reliant on plants. "It's of fundamental importance to understand how plants relate to global carbon cycles," said Blonder.