An international team of scientists has just returned from an expedition in the Pacific Ocean, where they collected samples of sediment, basalt lava flows, and other volcanic eruption materials to piece together the formation history of an ancient trail of underwater volcanoes known as the Louisville Seamount Trail.

The expedition, part of the Integrated Ocean Drilling Program (IODP), marks the beginning of a scientific journey to better understand processes occurring deep within the Earth that shape the features on the planet's surface such as seamounts, or ancient volcanic mountains in the sea. Tens of thousands of seamounts exist in the Pacific Ocean alone.

"During this expedition, we sampled many ancient individual lava flows and a fossilized algal reef. These samples will be used to study the construction and evolution of the individual Louisville volcanoes," remarked Anthony Koppers of Oregon State University.

Koppers led the expedition aboard the scientific research vessel, JOIDES Resolution, with co-chief scientist Toshitsugu Yamazaki from the Geological Survey of Japan at the National Institute of Advanced Industrial Science and Technology.

Over the last two months, the IODP Louisville Seamount Trail Expedition drilled 1,113 meters (3,651 feet) into the seafloor to recover 806 meters of mostly pristine volcanic rocks, making it one of the most successful research expeditions ever to recover this type of rock from the Earth's oceanic crust. The samples were recovered from six sites at five seamounts varying in age from 50 to 80 million years old.

"The sample recovery during this expedition was truly exceptional - I believe we broke the recovery record for drilling igneous rock with a rotary core barrel," added Yamazaki. A rotary core barrel is a type of drilling tool used for penetrating hard rocks.

Linear trails of volcanoes found in the middle of tectonic plates, such as the Hawaii-Emperor and Louisville Seamount Trails, are believed to form from a hotspot - a plume of hot material found deep within the Earth that supplies a steady stream of heated rock from depths as great as 2,900 km up to the surface. As the tectonic plate drifts over the hotspot, new volcanoes are formed - and old ones become extinct. Over time, a linear trail of these aging volcanoes is formed. The Louisville Seamount Trail is 4,300 kilometers (about 2,600 miles) long.

"Submarine volcanic trails like the Louisville Seamount Trail are unique because they record the direction and speed at which tectonic plates move," explained Koppers.

Scientists use these volcanoes to study the motion of tectonic plates, comparing the ages of the volcanoes against their location over time to calculate the rate at which the plate moved over a hotspot. These calculations assume the hotspot stays in the same place over time.

"The challenge," said Koppers, "is that no one knows if hotspots are truly stationary - or if they somehow wander over time. If they wander, then our calculations of plate direction and speed need to be re-evaluated."

"But even more importantly," he continued, "the results of this expedition will give us a more accurate picture of the dynamic nature of the interior of the Earth on a planetary scale."

Recent studies in Hawaii have shown that the Hawaii hotspot may have moved as much as 15 degrees latitude (about 1,600 kilometers or 1,000 miles) over a period of 30 million years.

"We want to know if the Louisville hotspot moved at the same time and in the same direction as the Hawaiian hotspot - our models suggest that it's the opposite, but we won't really know until we analyze the samples from this expedition," explained Yamazaki.

In addition to the volcanic rock, scientists on this expedition also recovered sedimentary rocks that preserve shells and an ancient algal reef - typical of living conditions in a very shallow marine environment. These ancient materials show that the Louisville seamounts were once an archipelago of volcanic islands.

According to Koppers, "we were really surprised to find only a thin layer of sediments on the tops of the seamounts and only very few indications for the eruption of lava flows above sea level. It seems that the volcanoes have only been at or above the surface of the ocean for a short amount of time - we weren't expecting this."

The IODP Louisville Seamount Trail Expedition wasn't solely focused on geology. More than 60 samples from five seamounts were collected for microbiology research, making the Louisville samples the largest collection of volcanic basement rock ever collected for microbiology research during forty years of scientific ocean drilling expeditions.

Exploration of microbial communities within the seafloor, known as the "subseafloor biosphere" is a rapidly developing field of research. Using the Louisville samples, microbiologists will study both living and relict microbial residents within the old sub-seafloor volcanic rocks from Louisville. They will examine population differences in the volcanic rock and overlying sediments and different kinds of lava flows. They will also look for population patterns relative to depth in the seafloor and between seamounts of varying ages.

Over the coming year, samples recovered during the IODP Louisville Seamount Trail expedition will be analyzed to determine their age, composition, and magnetic properties. Like a puzzle, this information will be pieced together to create a story of the eruption history of the Louisville volcanoes, which will be compared to that of the Hawaiian volcanoes to determine whether or not hotspots remain stationary over time.

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