Satellite eye on Earth: September 2017 – in pictures

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Algal blooms, hurricanes and volcano fields are among the images captured by Nasa and the ESA last month

A potentially harmful algal bloom covered more than 700 square miles in the western basin of Lake Erie in late September, turning the lake bright green and alarming residents and local officials. Blooms tend to thrive in Lake Erie during summer, sustained by warm water temperatures and nutrients from farm runoff. This year, the bloom had been ongoing since mid-July.

Photograph: MODIS/Terra/NASA

Autumnal leaves across the north-eastern United States. Conifers, which are evergreen, dominate the northern forests but patches of yellows and oranges can be seen throughout Canada and New England. Yellows and light tans predominate in Ontario, Canada, and in Michigan and the Midwestern United States. These more southerly areas are heavily agricultural, so the autumn colours may be influenced by drying crops such as hay and corn. The changing of leaf colour in temperate forests involves several causes and reactions, but the constant factors are sunlight and heat. As temperatures drop sooner and sunlight fades faster at higher latitudes, the progression of autumn colour changes tends to move from north to south across North America from mid-September through mid-November.

A68A iceberg in Antarctica
Credits: MODIS/Aqua and Terra/NASA

A 2,240 square-mile (5,800 sq km) iceberg split off from Antarcticas Larsen C ice shelf in July.

In September, scientists were able to get their first daylight looks at the iceberg named A68A.

Offshore winds had pushed sea ice away from the Larsen C ice shelf and out to sea. The remaining thin layer of frazil ice (grey mottled streaks on the dark ocean) does not offer much resistance, letting the icebergs move more easily about the ocean. The passage between A68A and the front of the ice shelf has already widened, and the smaller bits spread out.

Photograph: Sentinel-2A

The Sentinel-2A satellite captured this part of north-west England. The dark brown area near the centre of the image is the Forest of Bowland with its barren fells and peat moorland. In the upper left we can see some of the intertidal mudflats of Morecambe Bay, with the city of Lancaster on the coast. Preston is situated in the lower left on the River Ribble, which flows into an estuary where it meets the Irish Sea. The area north of the Ribble Estuary is the Fylde coastal plain, a square peninsula created by sediment deposits. Parts were once dug for peat, but today towns and agriculture cover the plain.

The Xingu River in northern Brazil
Credits: Enhanced Thematic Mapper Plus/Landsat 7 and OLI/Landsat 8 /NASA

This pair of images shows how a major tributary of the Amazon River has been dramatically reshaped by construction of the Belo Monte Dam complex on the Xingu River in northern Brazil. Construction began in 2011 and when the dam becomes fully operational in 2018, it will become the fourth-largest hydroelectric plant in the world.

Water in the Xingu River generally flows northward toward the Amazon River. In these views, however, it temporarily dips southward while flowing around a 100km river bend. Only about 20% of the original river flow now makes the journey around this bend.

The reduced flow has produced new dry areas, seen here as tan and orange. The drying is reported to have affected the aquatic life and a number of indigenous tribes living in the area.

The dam now diverts about 80% of the flow into the main reservoir, through a canal, and into a secondary reservoir.

Photograph: MODIS/Terra/NASA

The Amazon River rises in the icy glaciers of the Andes Mountains and winds across more than 4,000 miles (about 6,500km) across Peru, Bolivia, Venezuela, Columbia, Ecuador and Peru before reaching the delta. About 7.7 million cubic feet (219,000 cubic metres) pour into the Atlantic Ocean every second roughly 88 Olympic-sized swimming pools. Full of sediment and large amounts of organic matter, it forms a large plume of nutrient-rich, fresh water that extends well into the saline Atlantic. The plume has enormous impact on the near-shore ecosystem of the region, feeding colonies of phytoplankton that in turn feed a diverse population of fish.

Photograph: OLI/Landsat 8/NASA

The Potrillo volcanic field, New Mexico, is known as a planetary analogue site, a location that gives scientists the opportunity to test their instruments and theories in extreme conditions that approximate otherworldly environments.

Potrillo is considered dormant now, with its last volcanic activity occurring about 20,000 years ago. The areas lava flows, craters and cones makes it appealing to planetary geologists.

Catastrophic flooding in northern India, Nepal, and Bangladesh

During monsoon season, heavy rains regularly fall on south Asia. But the summer monsoon of 2017 was different. In August 2017, days of punishing rainfall caused catastrophic flooding in northern India, Nepal, and Bangladesh and more than 40 million people were affected.

One of the hardest hit areas was Bihar, a state in east India with a vast expanse of flat, fertile land. These two images show how Bihars waterways changed through the monsoon. The first image shows the area before monsoon rains began. The second image shows the Ganges, Koshi, and several other rivers after floodwater covered large swaths of the landscape.

Photograph: ISS/NASA/ESA

The Bosphorus, also called the Istanbul Strait, divides Europe (lower half of the image) from Asia (upper). Turkeys largest city, Istanbul, flanks both shorelines.

The Bosphorus enables significant amounts of international shipping to move between the Mediterranean Sea and the Black Sea. It is especially important as an outlet for Russian oil products. In this photograph, a few ships are visible in the waterway. At several points they need to make dangerously sharp turns, with coastlines obstructing visibility. The risks of navigating the Bosphorus are multiplied by the heavy ferry traffic linking the European and Asian shores. To reduce the number of ships and to improve safety in this narrow waterway just 1050m at the Bosphorus Bridge officials have proposed to dig a new waterway. The Kanal Istanbul would connect the Mediterranean and Black Sea at a point 70km to the west of Istanbul.

Photograph: VIIRS/Suomi-NPP/NASA

Dozens of wildfires burned across the western United States and Canada during September.

While it is unlikely that this season will be record-breaking for modern fire record keeping in the western United States, it is above normal relative to the last decade which has seen abundant fire activity, said John Abatzoglou, a fire researcher at the University of Idaho. Unusually warm and dry conditions fuelled the active fire season while a wet winter also contributed by triggering the growth of more grass in the spring which later turned into fuel for the fires.

Photograph: OLI/Landsat 8/NASA

The compelling scenery of the Bay of Kotor, in Montenegro, with its abundance of old churches, palaces, seaside villages and historic military fortifications, has become a major tourist destination.

The town of Kotor (population 22,000) now hosts hundreds of thousands of tourists each year, many arriving by cruise ship. In 2017, more than 493 ships dropped anchor near Kotor, bringing 535,000 tourists to the town and making it the third most trafficked port for cruise ships in the Adriatic.

Photograph: VIIRS/Suomi NPP/NASA

A line of three hurricanes two of them major and all of them threatening land brewed in the Atlantic basin in September 2017. Forecasters were most concerned about Irma, which was on track to make landfall in densely populated south Florida. Meanwhile, category 2 Hurricane Katia was headed for Mexico, where it was expected to make landfall on 9 September. And just days after Irma devastated the Leeward Islands, the chain of small Caribbean islands braced for another blow from category 4 Hurricane Jose. The image is a composite, showing cloud imagery combined with data on city lights.

Florida Keys National Marine Sanctuary

Hurricane Irma also altered the distribution of sand around the coast of Florida, as seen in these before and after images of the Florida Keys marine park. The light blue colour shows sediment suspended in the water, kicked up by the intensity of the storm.

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