Puerto Princesa Underground River and Palawan: 2011 Expedition Preliminary Report and Analysis

Introduction
The Saint Paul karst area and the Puerto Princesa Subterranean River have been the object of several geogprahical and caving expeditions carried out by the Italian Speleological Society (1989, 1991) and, later on, by the geographical association La Venta (2000, 2007, 2008). Some of the researchers have accompanied the project since the beginning.

During February-March 2011, La Venta has carried out another expedition, with the following aims:

• survey of the south-eastern region of the Saint Paul ridge.
• investigation of coastal cave systems (Little Underground River)
• exploration and survey of the Underground River eastern branches
• exploration and survey of the upper sector of Mount St. Paul
• exploration and survey of the Nagbituka region (northern part)

Puerto Princesa Subterranean River (PPSR)
The Puerto Princesa Subterranean River (PPSR) is composed by a main active branch (that is the underground river itself), for a total length of 8.2 kms. from the Inflow to the main entrance (Outflow), and a series of fossil (dry) upper galleries representing the ancient course of the river. The total development of the underground system, before the beginning of the expedition, summed up to 25 kms.

The exploration of a side branch discovered by the GAIA Exploration Club in 2003 has allowed the mapping of further 4.5 kms of huge galleries, named "150 Years" to recall the anniversary of the foundation of our country (1861-2011). Along these galleries, astounding calcite helictites (crystal formations) were discovered, so demonstrating that the PPSR, in spite of previous beliefs, is extremely important also from the point of view of speleothems (see Mineralogy and Speleothems).

Further exploration and mapping were carried out in other side branches of the cave, namely the Mud Galleries and the Australians' Inlet, for a total of approximately 2.5 kms.

Coastal explorations - The Little Underground River (LUR)
Northeast of the PPSR estuary, an entrance on the rocky coast gives access to a cave known since decades as the Little Underground River (LUR). The cave owes its name to its resemblance with the well-known PPSR, even if smaller in size.
The access to the cave is not easy and may be extremely dangerous in case of rough sea conditions, since the entrance is placed at the centre of a small bay, directly influenced by the waves and the tides. Due to this reason, the cave had never been seriously explored and mapped. The 2011 expeditions has led to the exploration and mapping of further 2 kms of galleries, so bringing the total development to over3 kms; the cave has not been completely explored, due to the rough sea conditions that have kept the team from further accessing the entrance.

Other cave explorations
Other caves were explored in the area of Nagbituka (North-east), in the Kwago area (South) and in the Binang Bangan massif (South-west).

Until 2010 the PPUR was supposed to be a cave with just "normal" chemical cave deposits (speleothems and cave minerals) of local or, maybe, regional importance as a maximum. But the exploration of 2011 proved that this karst system is exceptional worldwide also from this point of view. In fact, the PPSR hosts aesthetically astonishing speleotems (like the "calcite grass", an extremely rare kind of helictites and large transparent euhedral calcite rombohedroms inside pools at the bottom of gigantic orange flowstones; both these speleothems were discovered in the new parts of the "150 Years" Galleries). In the same cave, just a few tens of meters form the fossil sirenid along God's Highway, there is also a new type of speleothem, that we named "sail", a complex type of flowstone, the evolution of which was multiphase requiring stages in which water flowed by gravity followed by stages in which capillarity ruled (this formation is still under study.)

From the mineralogical point of view, the PPSR was known as hosting calcite and gypsum alone, but the first anlalyses carried out over the samples taken during the 2011 expedition evidenced that beside other minerals like strengite, iron and manganese oxides-hydroxides, the system hosts also at least one mineral new for the cavern environment: the Robertsite, a phospate related to the aggression of guano over the calcite speleothems. Another mineral new for the cavern environment seems also to be present janggunite (a very rare Manganese and Iron oxide-hydroxide).

The mineralogic studies are just at the beginning and we are confident that other cave minerals will be discovered in the PPSR


The effect of the tides inside the PPUR was already known, but in 2011 it was possible to realize a detailed bathimetric analysis of the system (from the entrance to Rockpile) in order to evaluate the amount of water present inside the system. In the meantime, automatic devices measured each 5 minutes for 6 days the level of the water, its temperature in three different sites (entrance, end of God's Highway and Rockpile). This will allow to carry out a quantitative calculation of the effect of the tides in relation with the amount of fresh water flowing inside the system: in this manner it will be possible to evaluate when the three layers of (sea, brackish, and fresh) waters will be destroyed by floods.

Water samples have been also collected their chemical content is under study.


During the Palawan 2011 expedition many different micro-meteorological researches were carried out. Their main purposes were:

1. To characterize the global air and water fluxes inside the cave.
2. To show the correlation between inflowing air fluxes and external meteorological conditions;
3. To measure air thermal sedimentations inside the cave, in order to show in the future their correlation with underground ecology;
4. To estimate the cave shape from airflow data;
5. To estimate the cave energetic in order t measure its sensitivity to touristic visits, and their impact on the cave.

We have obtained 190,000 internal wind speed measures, 3600 measure of external pressure and temperature data, and two temperature profiles of the cave, each with 20 measures with 0.01 degree Celsius of accuracy. The data collection is then really huge, and the analysis has just begun. Nevertheless we can already state some basic points.

Airflow
The internal airflow is very complex, mainly controlled by external temperature, but it is possible to see also dependences from pressure and external air humidity, an effect never studied before. Typical airflows are around 50-150 m³/s. For comparison, typical air fluxes of big caves around the world are 1 - 20 m³/s. The figure shows its direction inversions and its complex time variation of short time scale.




Temperature
The temperature profiles along the river show a sudden drop around x-2500 (near Crocodile-Gypsum galleries) where during our operations it was always possible to observe a stationary cloud. This seems to indicate that in this region there is a colder air inflow from upper galleries, possibly connected with branches discovered during Palawan 2011. The temperature variation in 11 days is less than 0.5 ºC, unexpectedly, concentrated in the most internal parts.




Energetic
Thanks to these measures and those of water level variations, we can estimate the water and air flow in the Subterranean River main branch. The average sea water flux is around 0.8 m³/s, the flux of river fresh water is 1 m³/s, with a typical temperature difference with cave of 2 ºC. In comparison, the airflow (100 m³/s. i.e. 100kg/s) is small.

The energetic flow is then mainly hydric, and can be estimated around 15 MW, an extremely high value. It's interesting to note that also the flux from animals is significant. Both Salanganes and bats have weights around 15-20 g each and a heat production of 0.2 W; therefore each million of these flying inhabitants releases 0.2 MW.

Tourism
In order to obtain from the tourist visits, an energy flux similar to the natural one inside the cave, around 150,000 people should stay continuously inside the cave. With an average visit duration of one hour. 3,600,000 people per day have to visit the cave to release the same energy of entering fluids. One million salanganes or bats spending half a day inside the cave give an energy flux comparable with 25,000 visitors per day. To estimate the human impact on the cave, it is necessary to study in detail these fluxes, which have a time and space dependence: to do this, we have left 2 data loggers inside the cave for a better estimation of its natural variability, but it looks that the receptive capacity of Puerto Princesa Subterranean River is surely enormous, and only insane human interventions (constructions, chemical changes, tunnels...) can damage the cave. Of course, the tourist visits should never take place during salanganes and bats diplacements into and out of the cave.

The new fossil branches discovered during our operation behave probably in a completely different manner. Their thermal relation with the river conduits is not clear; nevertheless the cave temperature profiles suggest that there are connection between upper and lower conduit levels.

They are not insluated conduit because a strong airflow is present there, but its intensity and behavior have not yet been measured. From the other side, there are no water or animal fluxes, then a huge and by far more accurate and two year long-work has to be done to understand them throughly.

As a first approach, we have left another temperature data logger inside these branches, to compare their yearly temperature range with that of the river conduits below. In the next months, we hope to have some better idea of their energetic behaviour, but many further studies have to be done.


During topographic surveys, many interesting morphologies have been observed and described.

The cave map itself allows us to describe the pattern of the cave recognizing the main evolutionary phases of this kart system. The new discoveries indicate a complex evolution under different condition of water flow. The interference effect between sea level changes and tectonic uplift is revealed by the presence of three main levels of cave passages.

Sea levels markers are present as water level notches at about 7.78 and 11-12 m above present sea level and as top-depositional surface of sediments. The interpretation of these markers is now in progress.


During the 2011 expedition, several water samples were collected, either cave waters or surface waters. The analyses will allow to estimate the surface and underground dissolution rate.

Organic elements are also important in order to explain the role of biological processes on the formation of some cave minerals.