Warning

Do not enter the water downstream of the Jim Jim Falls plunge pool. Estuarine crocodiles may be present.

Jim Jim Falls Earthcache

The Jim Jim Falls (Aboriginal: Barrkmalam) is a plunge waterfall on the Jim Jim Creek that descends over the Arnhem Land escarpment within the UNESCO World Heritage–listed Kakadu National Park in the Northern Territory. The Jim Jim Falls area is registered on the Australian National Heritage.

 The waterfall descends from an elevation of 259 metres (850 ft) above sea level via one drop that ranges in height between 140 and 200 metres (460 and 660 ft) into a plunge pool within the creek

Formation of the Falls

Waterfalls are commonly formed in the upper course of a river in steep mountains or escarpments. Because of their landscape position, many waterfalls occur over bedrock fed by little contributing area, so they are ephemeral and only occur during rainstorms. The further downstream, the more perennial a waterfall can be. Waterfalls can have a wide range of widths and depths, and this diversity is part of what makes them such a charismatic and interesting natural phenomenon.

When the river courses over resistant bedrock, erosion happens slowly and is dominated by impacts of water-borne sediment on the rock, while downstream the erosion occurs more rapidly. As the watercourse increases its velocity at the edge of the waterfall, it may pluck material from the riverbed, if the bed is fractured or otherwise more erodible. Hydraulic jets and hydraulic jumps at the toe of a falls can generate large forces to erode the bed, especially when forces are amplified by water-borne sediment. A process known as "potholing" involves local erosion of a potentially deep hole in bedrock due to turbulent whirlpools spinning stones around on the bed, drilling it out. Sand and stones carried by the watercourse therefore increase erosion capacity. This causes the waterfall to carve deeper into the bed and to recede upstream over time, the waterfall will recede back to form a canyon or gorge downstream as it recedes upstream, and it will carve deeper into the ridge above it. The rate of retreat for a waterfall can be as high as one and half meters per year.

Often, the rock stratum just below the more resistant shelf will be of a softer type, meaning that undercutting due to splash back will occur here to form a shallow cave-like formation known as a rock shelter under and behind the waterfall. Eventually, the outcropping, more resistant cap rock will collapse under pressure to add blocks of rock to the base of the waterfall. These blocks of rock are then broken down into smaller boulders by attrition as they collide with each other, and they also erode the base of the waterfall by abrasion, creating a deep plunge pool in the gorge downstream.

Streams can become wider and shallower just above waterfalls due to flowing over the rock shelf, and there is usually a deep area just below the waterfall because of the kinetic energy of the water hitting the bottom. Waterfalls normally form in a rocky area due to erosion. After a long period of being fully formed, the water falling off the ledge will retreat, causing a horizontal pit parallel to the waterfall wall. Eventually, as the pit grows deeper, the waterfall collapses to be replaced by a steeply sloping stretch of river bed.

Access to the Falls

The falls are located near the eastern boundary of the national park and 28 kilometres south of Jabiru. In the dry season, access from the Kakadu Highway is possible via a 60-kilometre gravel road, with the final 11 kilometres suitable for four-wheel drive vehicles only. However, during much of this period the falls dry up and do not flow. In the wet season when the falls are at their most spectacular, it is impossible to drive any vehicle into the area and are best viewed from the air.

The track in from the trailhead is marked with orange arrows to GZ but this is a rocky track requiring rock scrambling over boulders. Please stay on the signed track at all times

It is a 2km return walk through monsoon forest which will take you to a deep plunge pool surrounded by spectacular, 150-metre high cliffs.

This walk is suitable for people who are fit and can manage uneven terrain (large boulders, often slippery).

Allow 1 to 2 hours for this walk.

Visitors who choose to swim at the Jim Jim Falls plunge pool do so at their own risk. Please note the advice on visitor safety signs regarding crocodiles and all crocodile warning signs

Questions

Q1: What type of falls are Jim Jim Falls.

Q2: What is your estimated height of the falls?

Q3: Name three things you can see that are evidence of the above described process of the falls formation.

Hope you enjoyed this EarthCache & please feel free to upload a photo too.

Once you complete the Earthcache requirements you can post your find without delay, as per the guidelines. You will also need to verify your find by sending me an email providing answers to the questions. This can be through the message centre or via email linked in my profile.

References

http://jimjimfalls.com/Garnamarr-Campground-Jim-Jim-Falls-Region-Kakadu-National-Park-Australia.htm
https://topics.revolvy.com/topic/Plunge%20waterfalls&item_type=topic