The “Iceberg” Correction

Since leaving the Chilean coastline, the THOR team has been exploring the sea floor… with sound.  Similar to the way that sea mammals communicate with each other over long distances and submarines avoid obstacles, scientists use sound to “see” the bed surface and ultimately map the ocean bottom.   Sound waves are generated from beneath the ship from an instrument called a multibeam echo sounder which, in effect, is a giant loudspeaker pointing downwards and away from the vessel on either side.

Here’s how it works: the multibeam sends a “ping” (like you hear in the movies with submarines), a pulse of high-pitched sound that moves down and away from the bottom of the ship.  It’s called multibeam because each ping contains 432 individual depth soundings that go out in the shape of a fan. The angle and trajectory of each sounding, the time traveled and distance away from the source of sound, combined with the properties of the ocean, (temperature and salinity) are used to calculate the velocity of sound through water.  The result is a swath “image” of sound velocity, where the width of the swath is the maximum angle the outermost depth soundings have achieved as they travel some distance to the seafloor and back.

Each “ping” is displayed as a line of points. This image shows multiple pings. Each “ping” line is composed of 432 depth soundings – you may even be able to see the individual points.

For deeper water, the swath will be wider; for shallower water, the swath will narrow.  Each of the reflected soundings are then processed to show a continuous colorful ribbon, or snail trail, of the seafloor below the ship. (example snail trail image) The colors are equivalent to the distance the sound wave has travelled through the depth of the water, where the longest distances, which are blue, represent the deepest parts and the red colors are shallower features.  Collectively they “paint” a picture of the seafloor’s surface in 3-dimensions.

Most oceanographic research vessels employ the multibeam echo sounder whenever they can, the combined results of which can paint a detailed picture of processes that we could never witness ourselves through the depths of the ocean. Marine geologists, oceanographers, and glaciologists studying Thwaites Glacier will use this information to unravel the processes operating between the ocean and the ice shelves.  Features such as furrows and plough marks indicate past movement of the ice shelf and icebergs dragging along the sea floor, channels show where water flowed beneath past ice sheets, and high ridges or peaks may have been places where ice was once “grounded” (or resting on) the sea bed, a situation which may act to stabilize an ice shelf or glacier, and allay or even stop its’ backwards retreat.

The science team also use these echo sounders to make decisions about where to gather samples from the sea floor by producing an image of the layers of muds, sands, and rocks just below the surface. The samples help to decipher a longer history of how ice interacted with the ocean, and ultimately how the ice will behave in the future.  The accuracy of the data is critical to ensuring that the location where those samples are taken will not be in a place that might damage the instruments (coring devices) used to collect the samples.

An important part of collecting accurate multibeam data is accounting for a variety of physical parameters. On the ship, we are effectively a bobbing cork in the ocean. Combined with the echo sounder, a set of reference points are made with each “ping” to account for this unpredictable motion.  Similar to how a gyroscope works, the reference point data accounts for real time conditions such as roll (side to side) pitch (forward and backward motion), heave (the up and down motion) and yaw (the horizontal or side to side motion). The data processing software then applies clever corrections to make sure that the data accurately represent the true position and orientation of each sea floor sounding.

Two days after the ship’s passage through rough seas, THOR team members Kelly Hogan and Ali Graham noticed that the seafloor bathymetry data output suggested that the seafloor had a tilt when they knew it should have been flat.  In order to understand if the tilt was real, they needed to do an experiment.  They would have to go back over an area that had already been scanned, but in the opposite direction.  The difference in the two data sets would show an equal and opposite tilt (if they were right that the tilt was in error) and it would help them calculate the degree of that error.   In order to accomplish this, the seafloor would have to be flat and they would need about an hour’s worth of backtrack scanning of the same flat seafloor.

Icebergs are made of freshwater ice and compacted snow. They typically originate from the breakup of glaciers and ice shelves that terminate in the ocean.

 

Enter the icebergs.  The first significant iceberg that appeared was close enough to provide a terrific photo opportunity for the passengers, and the crew of Nathaniel B. Palmer made a spontaneous viewing loop around the iceberg.  (pic of the first berg) The ship had also entered the Bellingshausen Abyssal Plain in the Southeast Pacific Basin, the flattest area of the transit before reaching the Antarctic continental shelf, so the sea floor conditions were optimum.

Turn captured on the multibeam swath image.

Another iceberg on the horizon looked to provide the appropriate distance and time it would take to conduct the necessary scan.   Using that iceberg as a goal post, they made the first multibeam swath, rounded the second target iceberg (which was as photogenic as the first), and retraced the initial snail trail long enough to determine the degree of error and apply the correction.

These icebergs originated from Antarctica. They may be at least a year old, but their location in warmer waters will melt them very quickly, as much of their rounded surfaces are already showing.

Two icebergs later, the problem was solved and the colorful ribbon of seafloor bathymetry was returned to its horizontal self. These kinds of corrections are not uncommon and ensure that the data is good for when the THOR team reaches Thwaites itself, where the accuracy of the sea floor measurements will be important for selecting the best sea floor to sample and interpreting its history.

OTHER Icebergs…

Here are some of the other icebergs we have seen on our traverse through the Amundsen Sea. They have been categorized by shape, age, and how they formed.

This is classified as a blocky multi- year freshwater iceberg because of its steep sides and flat top.

 

 

 

 

 

 

 

 

 

 

 

Drift sea ice is young flat ice floes formed from sea water at the sea surface that can move with current or winds.

 

 

 

 

 

 

 

 

 

 

 

Landfast ice or “Fast” ice is multi-year flat, solid ice made of both seawater and fresh water (from snow) that is attached to the far continental margin and can include grounded icebergs such as the one in the background.

The J-Team

All field-based science conducted on board and beyond the Nathaniel B. Palmer would not be possible without the support of the Marine technicians.  They are in charge of on-board deck operations, ship to shore operations, and the safe deployment and recovery of scientists, scientific tools and equipment.

Within a day after leaving Punta Arenas, marine technicians Jennie Mowatt and Joee Patterson were tasked with the recovery of a state-of-the-art Autonomous Underwater Vehicle (AUV) that was being field tested in the Straits of Magellan prior to its deployment in the Amundsen Sea.

Jennie Mowatt will celebrate 4 years in her position in May; Joee Patterson, 3 years in May. They love their jobs and the great opportunity to problem solve. The work is always different, sometimes hugely frustrating but also hugely satisfying. They appreciate seeing Antarctica in ways most people never do. “We have seen the entire profile of the ocean around Antarctica- from the top to deepest depths. I have put my hands on creatures from 1,500 meters deep below the surface,” says Joee Patterson.

The pressure is on for the successful launch and retrieval of this “torpedo of science” that can accommodate up to 20 different sensors, including an obstacle detection sonar instrument in the nose cone.  The design is based on devices used by the petroleum industry and for national defense purposes; it takes advantage of the AUV’s ability to dive deep (up to 1,000 meters) but with payloads that will measure a variety of characteristics of the ocean, map the seafloor under Thwaites Glacier, and collect information on what is happening at the interface of both—something that was not possible until now.  Much was riding on this early test.

The morning of the test was perfect.  Cloudless skies were mirrored by the nearly still water of a small cove in the Straits of Magellan. The Hugin, built by the Kongsberg company (who also happen to provide the technology for multibeam bathymetry), is named for one of Odin’s ravens that travel the world to gather information.

 

 

 

 

 

 

 

Prior to launch, the science team meets with the entire Marine technician support group to go over safety and thesequence of activities. (pic of the big group) Jonas Andersson, one of the TARSAN scientists that manages the Hugin, rolls out the AUV from a specially made garage.

Once the bridle was attached and rigging set to lift Hugin off the ship, Joee and Jennie hopped in the zodiac to prepare for the AUV’s deployment.

With the Hugin in the water, the ship moves away and Jennie and Joee move in to watch over the AUV as it takes on water (shedding buoyancy) in preparation for diving.  Once it disappears, they return to ship.  Four hours later, the weather has turned ominous.  The skies are heavy, dark and spitting rain.  The winds have picked up and the sea surface is rough and rolling.  Hugin’s bright orange skin is spotted and Joee and Jennie are off in the zodiac to begin the process of bringing Hugin home.

Unbeknownst to those of us observing on deck, the marine technicians (known as the MT’s) had met and devised a plan, to include several contingencies for the AUV’s retrieval based on changes in the environment or equipment condition.  The first unplanned situation was the unexpected presence of a South American fur seal who found the AUV interesting.

“The seal was doing acrobatics while we were out there, and I thought it might jump in the zodiac. He came at us quickly and so I scooted the boat away, and then he just disappeared”, said Joee.

South American fur seal torpedoing through the air

Their first step was to attach the bridle system using the hooks on top that would be used to hoist the AUV onto the ship.  The plan was that one person would be in charge of maneuvering the lighter weight and buoyant zodiac while the other wrangled the two-ton AUV.

Assuming that the AUV would move more slowly and that the wind and the swells would impact the zodiac, their plan would take advantage of the zodiac’s maneuverability. The goal would be to tie the AUV to the side of the zodiac, which is a typical way of using a smaller thing to tow a larger thing. “Once we got out there, we figured out that our plan where one person did the maneuvering and one person to do the wrangling was not the optimum situation. The contingency was then to tow it astern of the zodiac. This presented other challenges.  The Hugin acts an anchor so we have to put a lot of power on the zodiac to get the Hugin to move at all.  Then once you get the Hugin moving you don’t want to get it moving so fast that it moves past you.  Add to that the swell and wind working against us as we try to keep a heading and keep it trapped behind us.”

 

Jennie summarized the complexity of the situation, “It was our first time working with the bridle system and we didn’t know how well the zodiac would travel with the AUV.  I definitely would not have predicted its hydrodynamic behavior as we tried to tow it behind the zodiac.  That was the thing that we couldn’t have predicted until we were actually doing it.”

 

 

 

 

Following the successful delivery of the Hugin to the deck, Jennie and Joee discussed adding a third person for next retrieval even if the conditions are calmer.  “It would be good to have more hands to pull the lines, and to use extra slip lines on the vehicle itself.  The weight of the bridal makes it want to sink, so keeping that in the boat will enable better control of the AUV.”

 

I was amazed at their perseverance and their calm under what was obviously difficult environmental conditions.  Yet for the J-Team, it was just another Friday at the office, and problem solving is why they are MT’s for science.

 

 

 

 

NBP’s Current Path Approaches the Second of Two Low Pressure Systems

Waves approaching 15 feet are regularly inundating both the lower and the main deck (where our berth is located).  Viewing the maelstrom from the large windows of the aft winch control room where I’m sitting, I can forget the sea sickness for a bit as I watch the incredible power and beauty of the sea, eyes fixed on the distant horizon as a rocking and rolling NBP slowly but very steadily works its way south.

Large wave on the starboard side of the aft deck.

It is after 12, and I realize I have missed lunch, when a message suddenly comes from the radio telling everyone outside to come in due to heavy seas.  Feeling somewhat normal, and wanting to know how fast or how close the ship is moving into the outer reaches of the severe weather (very cyclonic looking in my opinion), I head to the bridge.  To watch us float about with all the ease of a cork in a bathtub, you wouldn’t know that the NBP is a 6,800-long-tons (15,232,000 pounds) ship with 3,000 (10’ x 40’) steel plates (the bow plates are 1 9/16 inches thick) carrying 425,000 gallons of gas.

 

The image on the left is a computer model of the low-pressure system. The NBP is the red target between 1016 and 1012 pressure contours. Right image shows the ship’s traverse to the Amundsen sea.

 

Meanwhile, below deck, science planning and activities persevere.

 

The monitors show the depth from the multibeam generated sound wave to the seafloor, 4426 meters (13,278 feet) and the reflected signal from two views. The range of color indicate depth-blues are deepest and reds are shallowest. Chris Linden, the NBP multibeam manager and expert, points out the location of the transducers that generate the sound waves and the instruments that will receive the signals that have been reflected off the seafloor.

 

The THOR team and NBP multibeam specialist Chris Linden set up the EM122 multibeam echo sounder to start gathering bathymetry information. As soon as the ship passed beyond the legal border of Chile, they would take advantage of the adjusted ship traverse to gather high resolution seafloor bathymetry from an area that hasn’t been mapped previously. There will be some challenges to acquiring the return signal: the slow ship speed combined with the rough seas that impact the ship’s hull create interference around the receivers (bubbles, for example), affecting the quality of the data.

Other ITGC scientists, whose constitutions are more stalwart than mine, sit at workstations and tabletops that are festooned with pieces of anti-slide fabric (much like rubber carpet pads) utilizing predrilled holes for eye-screws to which bungee cords are tied; these go over top of valued electronics to hold them in place.

 

Author Elizabeth Rush is ready for the rough sea crossing!

 

Tilt-o-meter and barometer on the bridge of the NBP.

 

Back on the bridge of the NBP, I stumble around still developing my sea legs as the motion of the ship is amplified due to its height off the water. The near 360-degree view of the waves is both captivating and hypnotic, helping to subdue some of the seasickness.  In fact, sitting on one of the control chairs is like having an unlimited ticket on the earth’s most incredible amusement park ride.

But as we roll upwards of 20 degrees each way, knowing that the larger sea is coming, the amusement fades for a few moments.  THOR team member and PhD student Victoria Fitzgerald adds, “There is no getting off this ride.” According to Chief Mate Rick Wiemken, there is a buoy in the area that has measured a wave height of 80+ feet. The highest wave ever recorded!

 

 

 

 

NBP pitches forward into a large wave.

One would think TARSAN’s successful deployment of the Hugin AUV would appease Ran (the AUV’s unofficial name), the Nordic goddess of the seas.   The crew of the ship are reassuring: the storm will still pass in front of us.  And while we will see a couple more days of rough seas, the Palmer (with 80 research cruises since coming into service in 1992) will handle it, and we will have gained a deep appreciation and respect for the amazing people who are taking care of us, and the forces of nature around us that we hope to better understand.

First Things First

After 24 hours of travel from Houston, Texas to Punta Arenas, Chile, I arrived exhausted yet excited (and perhaps just a wee bit anxious of the unknown) to be part of something very unique.  My name is Linda Welzenbach and my role on this expedition is to share the scientific discoveries that will come from our journey to Antarctica on board the RVIB (research vessel/ice breaker) Nathaniel B. Palmer (NBP).  Akin to a spacecraft exploring new frontiers beyond Earth, the Nathaniel B. Palmer and her marine operations specialists will navigate safe passage through Antarctica’s icy waters for the 26 ITGC scientists and the wide array of science activities they have planned over the next two months.

This first post will bring you aboard to see what she has to offer, and how scientists become seafaring explorers.  NBP’s origins and history will be highlighted in a later post.

Welcome to the Nathaniel B. Palmer! She is a beautiful ship, with commodious berths…if you can find the one green door among many that is assigned to you.

The NBP’s vitals can be found on the USAP website HERE

Upon arriving Sunday evening, we discover that the ship would be leaving a day early. The NBP was thirsty and if we wanted to stay on schedule, we would need to leave for the “gas station” Monday evening.

Prior to departure, we head to the U.S. Antarctic Program warehouse for orientation and distribution of the necessary Extreme Cold Weather (ECW) gear.

Radio journalist Carolyn Beeler models the steel toed boots needed to work on deck and onshore.

We are on board for just a couple hours, yet the first task will be to participate in a simulated exit.  As part of that exercise, we must be able to put on flotation suits, which are required for situations that call for abandoning ship (below).  During the cruise we will practice several more drills of this nature, to build muscle memory in the event of a real emergency.

Interpretive dance is the best approach for getting into the flotation suit.

Dr. Rebecca Totten Minzoni (left) and her Ph.D. student Victoria Fitzgerald successfully complete the flotation suit challenge.

There are two covered life boats for passengers- each one can hold the full complement of scientists.

THOR scientist Dr. Alastair Graham in the surprisingly comfortable life boat.

In anticipation of an evening departure, we met in the laboratory to unpack and sort through all the core processing supplies, stowing them securely in anticipation of the rough seas that characterize Drake’s passage. To see live weather, and forecasts, click HERE.

THOR team members (l to r)- Rebecca Totten Minzoni, Alastair Graham, Rachel Clark, Rob Larter- sort through and distribute core processing supplies in the core processing lab. All drawers and cabinets have dog-locks to ensure they do not open during passage through rough seas.

A bit after 7pm, #NBP1902 left Punta Arenas to refuel.  As of this posting, we are back in Punta Arenas, and remain here until maintenance activities have been completed.

 

Linda is the science communications specialist in the Department of Earth, Environmental and Planetary Sciences at Rice University. She is a geologist and veteran of two expeditions to collect meteorites from Antarctica. Her role for THOR is public outreach, and so she will communicate science activities during the first scientific cruise in 2019-NBP19-02 and serves as the project webmaster.

Sea Ice at Thwaites Glacier

Like all good explorers who are preparing for the unknown, I went looking for information about what to expect in the place where we will spend the better part of two months. Thanks to Rob Larter who had tweeted information about the sea ice in December, I found Sentinel-1 SAR imagery imagery that shows the coverage as of TODAY! You can go see this for yourself at: https://www.polarview.aq/antarctic . #ThwaitesGlacier (on the grid at 75°30′S106°45′W) is the slight tongue extending out along the 106W gridline, and the area in front of it looks to be breaking up.

Image downloaded from Polar View

THOR 2019 Cruise News- THOR team gets ready to set sail for Antarctica

PATH OF THE NATHANIAL B PALMER THROUGH 24 JANUARY. FOLLOW NBP’S PROGRESS IN THE FUTURE HERE.

In just a little less than one week, the THOR (Thwaites Glacier Offshore Research) science team members (including EEPS science writer Linda Welzenbach) will embark on a two month cruise to the Amundsen Sea, Antarctica. The mission: collect sediment cores from the seafloor beyond Thwaites Glacier that record its past behavior. They will also collect ocean-floor sediments deposited at the current grounding line (the location where the current ice shelf is attached to the seafloor) that contain records of changes taking place in the glacier and the adjacent ocean (e.g. the last 10,000 years). The scientists will also use ship-based sounding and geophysics instruments to “see” the current and past topography of the seafloor and how it might influence present day ocean circulation near Thwaites Glacier. The information from this cruise and another that follows in 2021 will allow scientists to better assess the glacier’s current and future stability.

THOR will be working along side with TARSAN and GHC on a variety of tasks during the 53 day cruise.

EEPS emeritus faculty John Anderson and science writer Linda Welzenbach are part of an NSF-NERC research consortium called the International Thwaites Glacier Collaboration.   THOR is one of 8 teams whose combined interdisciplinary efforts will produce a comprehensive look at the past and present characteristics of the glacier, seafloor and surrounding ocean to better understand the impact of climate on glacier behavior.

THOR Team on the cruise: Rob Larter (Science lead), Rebecca Minozi (Rice alum), Kelly Hogan, Alastair Graham, Rachel Clark, Linda Welzenbach

Advocates For Science

From a steadily growing interest by the scientific community along with increased demand by educators and policy makers, science communication has become the need of the hour. The American Geophysical Union (AGU)  launched the Voices for Science Program to help the geoscience community meet those needs. The program aims to help train scientists from all stages in their careers to be better science communicators and advocates for public engagement.

With two different tracks, communications and policy, the Voices for Science program provides the opportunity to actively participate and explore different facets of science communication. Only 30 individuals were chosen  from a pool of 100 candidates to be a part of the inaugural program. Doctoral candidate Sriparna Saha has been selected as a part of the initial cohort for the communications track.

Read about the Voices for Science Program in the following article published in EOS:

Reach for the Stars STEM Festival 2018

The twelfth annual ‘Reach for the Stars Stem Festival‘ , co-sponsored by the Ride Family Foundation and Rice Space Institute, was held at Rice University on Saturday, April 21st. It was  a spectacular success. This festival, which targets middle school girls, includes a street fair, an inspiring talk by a woman astronaut, and roughly thirty women-led science and engineering workshops. The plenary talk was given by NASA astronaut Peggy Whitson, who also happens to be a Rice Alum. This event turned out to be another opportunity for the Rice Earth, Environmental and Planetary Sciences Department to showcase its commitment towards science outreach and education.

 

The EEPS exhibit table engaged young girls with fun, hands-on activities like the plate tectonics (using Oreo cookies), along with the tried and true rock and mineral identification.  Some of the modules presented were developed as a part of the EEPS Reach teaching program, and successfully kickstarted part of the workshop sessions. 


 

 

It was amazing to see that the young girls were ecstatic to learn about science- and geology in particular- even if some of the girls only cared about eating the Oreo cookie continents. Not just the young girls were engaged. Some of the teachers accompanying the girls actually took notes on the hands-on activities (the Oreo cookie plate tectonic activity was an instant hit with both young and old alike), telling us that they would incorporate them in their classroom teaching. Perhaps this is the beauty of public outreach activities, to be able to connect with people in such a way that they start to care about science.

Graduate students Alana Semple, Juliana Spector, Laura Carter and Sriparna Saha represented the department at this event and mentored two 45-minute workshops focused on the Earth’s Interior (Differentiation and Convection) and the Earth’s Exterior (Wet Texas: from Floodplains to the Coast).  Known formerly as the ‘Sally Ride Festival‘, this annual fair brings in hundreds of young girls to the Rice University campus, giving them a glimpse into the world of science in a way that excites them and encourages them to explore the world around them.

ESCI 321 &322 Field Trip: Tales of Mud Volcanoes, Evaporite Deposits and Lava Tubes.

 

This blog describes the 5-day field trip for the Fall 2017 ESCI 321 and 322 classes to Southern California from October 6 and 10, 2017. The trip was led by professors Cin-Ty Lee and Rajdeep Dasgupta, and reported by undergraduate students Kendra Baldwin, Kyle Bartsch, Simon Chan, Aitash Deepak, Jennifer Kroeger, Jason Mendez, Jared Nirenberg, Sarah Silberman, and Jackson Stiles. The group was assisted by graduate students James Eguchi, Damanveer Grewal, Hehe Jiang, Sriparna Saha, Chenliang Wu, and Dr. Ming Tang.

The Southern California region has a complex geologic past with subduction, rifting and strike-slip motion, occurring along the major plates underlying the North American Continent. Most of California’s Paleozoic geologic history is evident in regions of the Mojave Desert and Death Valley. The Paleozoic era saw deposition of limestones, sandstones, and shales that were later eroded, displaced or uplifted during the tectonic activity that followed in the Mesozoic and Cenozoic. The rocks are primarily limestone with an abundance of fossils that indicate the evolution of early marine life forms. The region saw multiple periods of sea level fluctuation that led to the deposition of carbonate reefs along what is today’s Death Valley.

The Mesozoic was a period of increased geologic activity. During the middle to late Jurassic period, the Farallon Plate began subducting beneath the North American Plate, leading to the development of an extensive volcanic-arc system along the western coast of North America, and uplift of the Rocky Mountains in the late Cretaceous. Subduction also led to formation of the Southern California Batholith and other plutonic and extrusive volcanic regions in the Mojave Desert Region. An example of Mesozoic plutonic rocks can be seen in the Joshua Tree National Park, where the extensively exposed rocks exhibit uniformity in texture and grain size. The peak of volcanic activity occurred during the late Cretaceous in the southern Sierra Nevada region. The region was also covered by sedimentary deposits, with uplifting and metamorphism combined to create intertwined sedimentary and volcanic deposits.

During the early Paleogene period, while Farallon Plate subduction continued, volcanic activity in the peninsular region ceased. Uplift and erosion rates were continuous, which led to the deposition of vast amounts of sediments along the western continental shelf. Moving into the early Neogene period, the Farallon Plate disappeared into the subduction zone forming the San Andreas Fault; at an angle oblique to the western margin of the continent. As mountains began to rise along the coastline, marine sedimentary deposits became exposed. Eastward, crustal thinning and tectonic uplift along the Mojave desert region led to the development of the basin and range landscape. Additionally, Baja California started to move westward, away from Mexico.

In the quaternary period, the major driver of tectonic activity is the strike-slip San Andreas Fault, resulting in transverse ranges and extensional regions. Modern Rivers flowed through the basins while there was still volcanic activity in the Mojave region.

Day 1

The first stop of our trip was at Tourmaline Beach in La Jolla, California. We looked at the Point Loma Formation, which consists of marine deposits of sandstone and siltstone, formed originally in the Sierra Nevada- Peninsular Ranges batholith during the late Cretaceous. These were eroded from the roof of the magmatic arc that rose quickly due to compression and magmatism. Rapid erosion and transport of the deposits can be implied from the poorly rounded igneous sand grains. The marine deposits of forearc sandstones are tilted; graded-bedding and small areas of soft-sediment deformation are visible here.

Day 2

Marine depositional layers at Tourmaline Beach Photo Credit: Jackson Stiles

San Diego River Upper Estuary

 After a breakfast of bagels we reached an overlook above the San Diego River. The river is slow moving, and while the water level was fairly low when we were there, we could tell that the water level is often much higher. The water here is estuarine and thus brackish, but does not have strong enough sediment discharge rate to create a full delta. The sediment load is mostly comprised of fine sands and silt.

Hospitality Point-San Diego River Mouth and Lower Estuary

 Following the San Diego river overlook, we made our way to where the river meets the sea. While the San Diego River has migrated along the coast over time, it is now contained by a jetty, cementing its path to the ocean at one spot. The engineered jetty also prevents beach sediments carried by currents along the shore from piling up in mission bay in favor of generating a large sandbar at the river channel. This piled up sediment is rarely breached by floods and suffers minimal erosion.

Sunset Cliffs Next, our group stopped at the cliffs overlooking the Pacific Ocean at Point Loma. These cliffs are an example of late Cretaceous sandstones (75ma) that have a high sand to mud ratio, making them fairly resistant to erosion. These sandstones belong to a forearc setting, exposed due to tectonic uplift, that enabled preservation and exposure of deep water sediments. Finely laminated layers at the bottom of the exposed strata are most likely the result of deposition in a calm depositional environment with high clay content. Overlying the thin laminated layers was a thicker layer of sandstone (indicating a much higher energy environment) and the white markings are erosional surfaces along the cliffs. Within this layer  large rip-up mud clasts were deposited. Further up in the outcrop we could see an old soil horizon and erosional unconformity that represents a 70 million year gap between the Cretaceous sediments and the more recently deposited sediments. We also identified sections of soft sediment deformation and local slumping from differential compaction of the overlying layers on the soft sediments. The entire outcrop was interlaced with faults.

Soft sediment deformation overlaying clay layers.  Photo Credit: Jackson Stiles

Coronado Overlook

 Our next stop was at the top of the Cabrillo National monument overlooking the San Diego Bay. The bay itself is a graben bound by faults on the west, and the Cretaceous mountains in the East. Coronado Island is a sand spit created by long-shore sediment pulses from the ocean. The sediment deposited on the coastal plains from the eastern mountains is manifest into turbidites and deep water deposits.

Peninsular Ranges Batholith-Cretaceous Plutonic Rocks

Outside of San Diego, we parked along the roadside to look at a large outcropping in the Peninsular Ranges batholith region, which is around 90 million years old. At the road cut the majority of the rocks were tonalite (a type of felsic granodiorite mostly made of plagioclase). This tonalitic outcrop was crosscut by large dark colored (mafic) and light colored (silica-rich) dikes. The dikes intruded after the tonalite batholith had formed and the brittle nature of the tonalite led to the development of extensive fractures.

Cuyamaca Lake

Cuyamaca Lake is underlain by Cretaceous gabbro composed mostly of plagioclase and orthopyroxene that are associated with the Cretaceous volcanic arc. Olivine was also present, but it was difficult to identify. The rocks around Lake Cuyamaca are also about 90 million years old, but is unique given it is one of the only sites in all of Southern California with layered gabbro deposits.

Jurassic Migmatites

 To reach this location we took a quick hike through the bush.  Exposed on the plain beyond were Paleozoic aged sedimentary rocks that had been melted and deformed during the Mesozoic era by through ductile underthrust in a subduction zone. During this process, many felsic (white colored) dikes formed through the rock, cross-cutting each other in several places. Within these dikes, we observed clusters of black coarse-grained tourmaline crystals; these are described as tourmaline pegmatites. Throughout the surface of the exposure, there were small, unnatural depressions which interestingly served as evidence that the outcrop was used by Native Americans to grind nuts.

View of Alluvial Fan
After leaving Julian (without having any of their famous apple pie), we stopped along the side of the road in a vast plain surrounded by mountains. The region showed a high quantity of brittle shear within fault gouges, and ductile shear visible in mylonite metamorphism resulting from high shear strain. Protomylonites from this intense ductile shear were quite prominent. The tonalite in this area was highly foliated, and there were few dikes present. The alluvial fans observed here had a high inclined gradient and contained many boulders and cobbles. The vast plain was actually a large coalescence of alluvial fans known as a bajada.

Two cross-cutting dikes in the Jurassic Migmatites.  Photo Credit: Chenliang Wu

 At the next stop, we were greeted by a small shack with the words “dead body inside” crudely painted on it. The stop was located at the base of the mountains near Anzo Borrego, with a view of a range across a playa. The mountains in the distance had reddish black sediment deposits along their hillsides. These were representative of fluvial sediments about 3 to 5 million years. The reddish black coating was likely a layer of iron-manganese oxide around 10 microns thick, and it indicates they were older than the incision. The rocks along the hillside we had stopped at were proto-mylonites. The shear stress during the mylonitization process caused various minerals in the rock to recrystallize that resulted in presence of clusters of garnet crystals forming throughout the matrix. The mylonitization was an inter-arc shear zone and most likely occurred during the late Cretaceous arc magmatism, and suggests a connection between the arc magmatism and a great amount of deformation of the upper plate.

Day 3

Salton Sea Area

 Our first stop on the third day was at the Salton Sea Pliocene deposits between the Salton Sea and the Gulf of California Basin. The deposits were fluvial, lake, and deltaic associated with the initiation of the rifting of the Gulf. We saw different surfaces, including tilted mudstones with sandstones on top of them. The canyon had large cobbles around the rim, likely transported there by large floods. Many of these cobbles were mylonites similar the ones we saw at the end of Day Two.

Our next stop was at the Salton Sea which is a landlocked water-body, formed as a result of northward extension of the Gulf of California, to accommodate the developing faults in the area. While the base of the Salton Sea is oceanic crust, the water itself is not that deep (~10s of meters). Interestingly, the Salton Sea is about 234 feet below sea level. Over the last 100,000 years or so, the water level has been decreasing continually. The restricted nature of sea lead to conditions with no upwelling, and therefore there is no thermohaline circulation that caused the sea to stratify and there is a good amount of bioactivity in the top layers. Every once in awhile this circulation will start up, and many of the fish die. The sea is now fed by agricultural runoff.

Obsidian Butte Outcrop

 Here we had the chance to see what was left of a rhyolitic, Pleistocene lava flow that quenched to obsidian. Rocks layered with obsidian and pumice and xenoliths were interesting features at this outcrop. These features indicate that an initially volatile-rich magma was subjected to decrease in pressure which led to the formation of these layered obsidian-pumice flows. As the volatiles began to escape, the magma was left with little/no gas and it quenched eventually to form glassy obsidian. The escape of bubbles was in fact facilitated by their size. The smaller bubbles that could not escape eventually formed the pumice layers. We also evidence of shearing and slow stirring of the magma at the surface. The rhyolites indicate that this area tends to have a high heat flow and a thin crust.

Presence of mud-volcanoes in the area, further establish the dominance of a high geothermal gradient in this area. These mud volcanoes are interesting because they are constantly migrating.The mud-volcano flows are essentially like basaltic lava flows, that flow slowly, traveling over larger distances owing to their low viscosity. The tops of the volcanoes were spurting out mud and bubbling out CO2.

Box Canyon

Tilted sandstone layers.  Photo Credit: Jennifer Kroeger

At Box Canyon, we observed tilted sandstone layers from the Pliocene with some conglomerates in the layers. These sandstones were tilted as the Gulf of California subsided during rifting. We saw evidence of cross-bedding and several channels indicating that most likely they formed in a braided river system. There was high grain size variability is the sandstones and conglomerates, so the depositional environment was likely close to the source. Also, we noted that gypsum was later precipitated in the fractures in the sandstone after deposition. Rip-up mud clasts were also found in both the sandstone and conglomerate indicating a high energy environment.

Mecca Hills

 At Mecca Hills, we stopped on the side of the road to observe a large anticline on the side of one of the hills. The sediment layers were most likely around 3 million years old, while the anticline was due to younger, active tectonics.

Pelona schist

 We stopped along the side of a highway dodging speeding vehicles, to observe the Pelona Schist that formed as part of the accretionary complex as the Farallon plate was subducting during the late Cretaceous period. The schist here underwent greenschist-facies metamorphism as is evidenced by the abundance of chlorite, biotite, and muscovite minerals. The rocks sections were well foliated and weathered on the top.

Joshua Tree – Jumbo Rocks

  At Joshua Tree National Park, we observed the Jumbo Rocks that are coarse-grained granites formed in the Cretaceous and Jurassic eras. Interestingly, the rocks are extremely homogeneous in composition and grain size without much texture. The rocks are jointed, that likely formed while the pluton was cooling to release stress. The joints were filled by dikes that had a very similar composition to the surrounding rocks, though we observed less biotite in the dikes. These dikes are possibly the remains of the magma that formed the pluton that came back up later to fill the joints after the joints formed during cooling.

Palms Canyon Oasis The last stop of the day was at Palms Canyon Oasis, where we observed Jurassic quartz monzonites with grey feldspar megacrysts. Here we observed large, single crystal alkali feldspars that were prominently larger than the surrounding grains. While it is not well-established how these megacrysts form, it has been proposed that fluid transport aided in the growth of these large phases.

Day 4

Salt Deposits
At this stop, we walked out on evaporite deposits. The evaporites were seemingly most NaCl but presumably had some amount of lithium and calcium chloride as well. The deposition of these evaporites is aided by the topography of the area.

 

Wind created evaporite formation. Photo Credit: Jackson Stiles

The area is a local low: structurally a small graben bounded by faults and mountains on either side drain into it. Water draining from the surrounding mountains enrich the water in minerals that then form evaporite beds as the water accumulates and evaporates in the graben. We also saw several interesting structures in the evaporite deposits including hair like structures formed by wind, beautiful halite crystals, and thin layers of evaporite formed on the surface of bubbles of briny water.

 

Vesicular rocks. Photo Credit: Jackson Stiles

Amboy Crater
At Amboy Crater, we looked at a cinder cone volcano and the associated extensive basalt lava flow. The cinder cone and basalt lava flow formed in the Pleistocene and their young age is reflected by the characteristic shape of the cinder cone as weathering has not changed its form much yet.  The extensive basalt flows seen here flowed over much larger areas than the rhyolite flows we previously saw due to the basalt having less silicate in it which lowers the viscosity allowing the lava to flow further. We examined bombs and other debris shot out from the cinder cone during its formation, although we did not actually walk up to the cinder cone itself.

The flow and pyroclasts were quite vesiculated and several flow indicators like ridges and folds visible. The cinder cone itself formed as lava was spit out of the vent as opposed to the usual flowing lava that would create other types of volcanoes. The cinder cone is formed as lava cools quickly after being launched into the air and falls back to the ground creating the characteristic conical shape made up of pyroclastics.  

Dish Hill

 Dish Hill was another volcanic cinder cone nearby; however, it was a few million years older. Due to weathering, and from mining for road fill, faces of this cinder cone had been dissected which allowed us to examine the interior structure of a cinder cone. Extensive weathering and oxidation also gave Dish Hill a reddish color rather than Amboy Crater’s black color.

Olivine and pyroxene xenoliths from the mantle. Photo Credit: Chenliang Wu (L: peridotite xenolith) and Jackson Stiles (R: pyroxenes)

At this stop, we saw more bombs and pyroclasts, both of which were larger for the most part. The dissected side of the cinder cone gave us access deeper into the cone where we found many peridotite xenoliths brought up from the mantle. We also saw granitic xenoliths from the crust that were brought up from the walls of the magma chamber and vent. Common in the rocks were olivine and pyroxene xenoliths.

Kelso Dunes

The Kelso dunes make up the largest field of windblown (aeolian) sand deposits in the Mojave Desert. The field is still active and includes migrating dunes, vegetation-stabilized dunes, sand sheets, and sand ramps. The grains are light-colored which leads to the conclusion that the protoliths are quartz and feldspar. A closer look at the grains themselves shows that they are fairly round and around 100 microns in the maximum dimension. These sand grains most likely originate from the Mojave River sink (west of the dune’s location). We also observed that the ripples on the dune face indicated wind direction, with the shadowed ripple portions on the lee face towards the wind. The south side of the dunes also held more vegetation than the lee side.

Cima Volcanic Field

Interior of a lava tube. Photo Credit: Chenliang

This volcanic field is made up of alkali basalt cinder cones and lava flows. These are associated with the development of the  Basin and Range. Most of the lavas in this area are younger than one million years.  The lack of erosion of the cinder cones and unweathered lava flows show the youth of these volcanoes. The lava tubes present in this field would have formed when a low-viscosity lava flow developed a hard crust (due to cooling of surface lava) that acted as a roof allowing the lava beneath to sustain high temperatures and continue flowing. Within the tube, marks, called flow ledges/lines, on the wall indicate different levels at which the lava flowed. Additionally, lavacicles (stalactites) and drip stalagmites are clearly visible inside of the tube. These could form when lava splashes onto the roof of the tube and slowly oozes down.

Mountain Pass Syenites

At this mountain pass, a carbonatite-syenite complex is approximately one billion years old. There is a mine nearby that extracts rare-earth elements from the carbonatite. Carbonatites are rare igneous rocks but have three models to explain their formation. Carbonatites are usually associated with undersaturated (low silica) igneous rocks; instead of silica tetrahedra, the anions are carbonate complexes. This rock can form directly by low-degree partial melts in the mantle, and melt differentiation. Another way is through liquid immiscibility between a carbonate melt and a silicate melt. Finally, extreme crystal fractionation may saturate CO2 levels in the magma, leading to the formation of carbonatites. Fun fact!: Mountain Pass used to be the largest rare-earth element mine in the world until China discovered large deposits which can produce up to 105,000 MT of rare earth minerals a year.

At this pass, we observed syenite (intrusive plutonic rock) with high amounts of orthoclase, along with minor amounts of hornblende and biotite.

Day 5
Red Rock Canyon State Park

The reddish rocks are Jurassic age sandstones that represent fluvial, lacustrine, and Aeolian environments, most likely having formed in a shallow, continental sea. The sandstones are overlain by gray Cambrian limestones. A closer look revealed that below the Jurassic sandstones lay Permian sandstones. These actually formed from large dunes, resulting in cross-cutting beds and dipping in a massive scale.

Aeolian Jurassic dunes. Photo Credit: Jackson Stiles

Late Cretaceous-early Tertiary back arc thrusting resulted in an inverted sedimentary sequence where older rocks are underlain by younger rocks during a retro-arc thrust event where the Farallon oceanic plate was being subducted beneath the North American plate.