Images

Time-averaged image, or “timex,” created by averaging the intensity of light recorded at each spot, or “pixel,” during a 10-minute video taken at Santa Cruz, California, on May 6, 2017. Blurred white zones show where waves are breaking. Line between wet and dry sand shows the maximum height on the beach reached by the waves (“runup”).

“Variance” image produced from video shot at Cowells Beach in Santa Cruz, California, on May 6, 2017. The more the light intensity changes at a given spot, or “pixel,” during the video, the brighter the value assigned to that pixel. Motion tends to produce changes in light intensity. Note bright areas along and beyond the shore where waves were breaking.

Snapshot, or first frame of from a 10-minute video taken May 6, 2017, in Santa Cruz, California.

Provisional data subject to revision. From the USGS Remote Sensing Coastal Change Project, illustration describes how the USGS measures topographic change with 4D photogrammetry utilizing the techniques of Warrick et al., 2017. A digital terrain model of a coastal cliff is shown with its ground control points.

Scientists from the USGS St Petersburg Coastal and Marine Science Center (SPCMSC) capture the smooth water of the tidal creek reflecting a pastel sky and soft clouds while heading out for field work at early dawn.

• Scenic photograph of Grand Bay estuary taken from a boat just before sunset following a day in the field.

After mixing about 20 grams of a sediment sample with distilled water, we add strong hydrogen peroxide to break down or "digest" organic matter that may be in the sample. Organic matter makes clay particles stick together and we need them separate in order to calculate accurate particle size fractions of the sample.

Tips of Brazilian waterweed (Egeria densa) break the surface at low tide in Lindsey Slough in the northern Sacramento-San Joaquin River Delta. More commonly, this invasive plant is completely submerged.

On March 21, 2017, the sediment trap from this instrument package (deployed the previous October into Monterey Canyon) is gone and the mounting frame is mangled, having been exposed to several significant turbidity currents in one deployment. 

Scientists deploy a Chirp seismic instrument from the beach. Seismic data provide view of sub-seafloor geology, which records depositional and erosional events and reveals geologic controls on sediment supply.

We add about 20 grams of sediment from a sample to distilled water for particle size analysis. Then we add strong hydrogen peroxide to break down organic matter that makes clay particles stick together. Digestion takes place overnight.

At the USGS Pacific Coastal and Marine Science Center, we have 3 WS Tyler RX-29 Ro-Taps that can dry-sieve coarser samples. This machine automatically rotates and taps the stack of sieves, so that smaller sediment falls through to the next sieve. Weighing the sediment trapped in each sieve gives us sediment size fractions.

The UIC CM5230/CM5015 analyzes total inorganic carbon content. It's less automated than other analyzers, but often easier to use.

We slip split cores into a labeled D-tube, and both are stored on specialized core racks in a walk-in sample refrigerator. USGS and non-USGS scientists often use our core and sample archives for new research. Contact the lab manager for access policies and other details.

We take most cores and samples straight from the loading dock into a large walk-in refrigerator (about 780 square feet), kept at the international core curation standard of 4° C plus or minus 2° C. Each core and sample must be labeled with an identifier and metadata, which follows the material through processing and analysis.

Washing a sediment sample through two sieves with distilled water lets us measure the fractions of gravel (bigger than 2 millimeters or -1 phi) and sand (2 millimeters to 63 microns, -1 phi to 4 phi). Smaller sediment passes through the sieves into a standard 1-liter graduated cylinder.

Lab technician Angela Tan takes a sample of the sediment suspended in liquid, for analysis in one of several ways.

The Beckman Coulter LS 13 320 uses laser diffraction to automatically analyze sediment size fractions between 2 millimeters and 0.35 micron (-1 phi to 11.5 phi).

The settling tube is filled with water and a pre-weighed sediment sample of mixed particle sizes is poured onto this brass "gate" at the top of the tube. When the operator flips the switch, the gate opens quickly like a venetian blind, releasing the whole sediment sample into the water column at the same time.

After adding a little sodium hexametaphosphate dispersant, we use a plunger to carefully stir the cylinder then let it settle, to ensure good mixing and standardized suspension of the sediment.

We can use the tried-and-true method of washing samples through finer and finer sieves, then weighing the sediment trapped in each sieve, to determine sediment size fractions.